Device for processing signals from a pressure-sensing touch panel

ABSTRACT

A device (116) for processing signals from a projected capacitance touch panel (43) is described. The projected capacitance touch panel (43) includes a layer of piezoelectric material (9) disposed between a number of sensing electrodes (7, 27) and at least one counter electrode (8). The device (116) includes a capacitive touch controller (84) having a number of measurement ports (122). The device (116) also includes a number of charge amplifiers (123). The device (116) also includes a number of terminals (C1, . . . , C5, D1, . . . , D5) for connection to the sensing electrodes (7, 27) of the projected capacitance touch panel (43). Each terminal (C1, . . . , C5, D1, . . . , D5) is connected to one of the measurement ports (122). Each terminal (C1, . . . , C5, D1, . . . , D5) is also connected to an input of one of the charge amplifiers (123) via a corresponding switch (SW) of a number of switches (117a, 117b). The device (116) also includes a controller (121) configured to synchronise the capacitive touch controller (84) and the number of switches (SW, 117a, 117b) so that during a first portion ([t1, t2]) of a cycle the capacitive touch controller (84) outputs a capacitance measurement signal (91) to one or more of the terminals (C1, . . . , C5, D1, . . . , D5), and the plurality of charge amplifiers (123) are disconnected from the terminals (C1, . . . , C5, D1, . . . , D5) by the respective switches (SW, 117a, 117b). The controller (121) is also configured to synchronise the capacitive touch controller (84) and the number of switches (SW, 117a, 117b) so that during a second portion ([t2, t7]) of the cycle the capacitive touch controller (84) does not output the capacitance measurement signal (91), and one or more of the charge amplifiers (123) are connected to the corresponding terminals (C1, . . . , C5, D1, . . . , D5) by the respective switches (SW, 117a, 117b).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 16/057,771, filed Aug. 7, 2018, which further claims thebenefit of priority from United Kingdom Application 1712720.0, filedAug. 8, 2017, each of which are incorporated by reference as if fullydisclosed herein.

FIELD OF THE INVENTION

The present invention relates to a device for processing signals from apressure-sensing projected capacitance touch panel, and to a touch panelsystem including the device.

BACKGROUND

Resistive and capacitive touch panels are used as input devices forcomputers and mobile devices. One type of capacitive touch panel,projected capacitance touch panels, is often used for mobile devices. Anexample of a projected capacitance touch panel is described in US2010/0079384 A1.

Projected capacitance touch panels operate by detecting changes inelectric fields caused by the proximity of a conductive object. Thelocation at which a projected capacitance touch panel is touched isoften determined using an array or grid of capacitive sensors. Althoughprojected capacitance touch panels can usually differentiate betweensingle-touch events and multi-touch events, they suffer the drawback ofnot being able to sense pressure. Thus, projected capacitance touchpanels tend to be unable to distinguish between a relatively light tapand a relatively heavy press. A touch panel which can sense pressure canallow a user to interact with a device in new ways by providingadditional information about user interaction(s) with the touch panel.

Different approaches have been proposed to allow a touch panel to sensepressure. One approach is to provide capacitive sensors which include agap whose size can be reduced by applied pressure, so as to produce ameasurable difference in the mutual capacitance. For example, US2014/043289 A describes a pressure sensitive capacitive sensor for adigitizer system which includes an interaction surface, at least onesensing layer operable to sense interaction by mutual capacitivesensing, and an additional layer comprising resilient properties andoperable to be locally compressed responsive to pressure locally appliedduring user interaction with the capacitive sensor. However, the needfor a measurable displacement may make it more difficult to use anexterior glass surface, and may cause problems with material fatigueafter repeated straining.

Other pressure sensitive touch panels have proposed using one or morediscrete force sensors supporting a capacitive touch panel, such thatpressure applied to the capacitive touch panel is transferred to one ormore sensors located behind the panel or disposed around the periphery.For example, US 2013/0076646 A1 describes using strain gauges with aforce sensor interface which can couple to touch circuitry. WO2012/031564 A1 describes a touch panel including a first panel, a secondpanel, and a displacement sensor sandwiched between the first panel andthe second panel. The displacement sensors, such as capacitive orpiezoresistive sensors, are placed around the edge of the second panel.However, it may be difficult to distinguish the pressure of multipletouches using sensors located behind a touch panel or disposed aroundthe periphery.

Other pressure sensitive touch panels have been proposed which attemptto combine capacitive touch sensing with force sensitive piezoelectriclayers. For example, WO 2009/150498 A2 describes a device including afirst layer, a second layer, a third layer, a capacitive sensingcomponent coupled to the first layer, and a force sensing componentcoupled to the first layer and the third layer and configured to detectthe amount of force applied to the second layer. WO 2015/046289 Atdescribes a touch panel formed by stacking a piezoelectric sensor and anelectrostatic sensor. The piezoelectric sensor is connected to apressing force detection signal generation unit, and the electrostaticsensor is connected to a contact detection signal generation unit.However, systems which use separate electronics to sense changes incapacitance and pressures may make a touch panel more bulky andexpensive. Systems in which electrodes are directly applied or patternedonto a piezoelectric film can be more complex and expensive to produce.

WO 2016/102975 A2 describes apparatus and methods for combinedcapacitance and pressure sensing in which a single signal is amplifiedthen subsequently separated into pressure and capacitance components. GB2544353 A describes apparatus and methods for combined capacitance andpressure sensing in which a single signal is separated into acapacitance signal, and a pressure signal which is amplified.

SUMMARY

According to a first aspect of the invention there is provided a devicefor processing signals from a projected capacitance touch panel, thetouch panel including a layer of piezoelectric material disposed betweena plurality of first electrodes and at least one second electrode. Thedevice is configured, in response to receiving input signals from agiven first electrode, to generate a pressure signal indicative of apressure applied to the touch panel proximate to the given firstelectrode and a capacitance signal indicative of a capacitance of thegiven first electrode. The device includes an amplifier configured togenerate an amplified signal based on the input signals. The device alsoincludes an analog-to-digital converter configured to be synchronisedwith the capacitance signal, and to generate the pressure signal bysampling the amplified signal at times corresponding to the amplitude ofthe capacitance signal being substantially equal to a ground, commonmode or minimum value.

The times for sampling the amplified signal may correspond to thecapacitance signal being within ±100 μv, within ±1 mV, within ±2 mV,within ±5 mV, within ±10 mV, within ±20 mV, within ±50 mV or within ±100mV of a ground, common mode or minimum value of the capacitance signal.

The device may be configured to drive an electrode of the touch panelusing a capacitance measurement signal, such that the input signalsreceived from a given first electrode vary in dependence upon acapacitive coupling between the given first electrode and thecapacitance measurement signal, and in dependence upon a strain of thelayer of piezoelectric material proximate to the given first electrode.

The capacitance measurement signal may be for measuring aself-capacitance of a given first electrode. The capacitance measurementsignal may be for measuring a mutual capacitance between the given firstelectrode and another electrode.

The device may be configured to generate a synchronisation signal independence upon the capacitance measurement signal. Theanalog-to-digital converter may be configured to sample the amplifiedsignal in dependence upon the synchronisation signal.

The device may be configured to generate the synchronisation signalincluding an offset with respect to the capacitance measurement signal.The offset may be determined in dependence upon a phase differencebetween the capacitance measurement signal and the input signalsreceived from the first electrode.

The device may also include a second analog-to-digital convertorconfigured to generate a digitised amplified signal by sampling theamplified signal. The device may also include a controller configured togenerate the capacitance signal based on the digitised amplified signal.

The analog-to-digital converter may be configured to generate thepressure signal and a digitised amplified signal sequentially. Theanalog-to-digital converter may be configured to generate the pressuresignal by sampling the amplified signal at a first sampling frequency,f_(piezo). The analog-to-digital converter may be configured to generatethe capacitance signal by sampling the amplified signal at a secondsampling frequency, f_(cap), which is greater than the first samplingfrequency. The device may also include a controller configured togenerate the capacitance signal based on the digitised amplified signal.

The controller may be configured to generate the capacitance signal byapplying a high pass filter to the digitised amplified signal. Thecontroller may be configured to generate the capacitance signal based onone or more recently obtained values of the pressure signal.

The device may also include a capacitive touch controller. The devicemay also include a signal separation stage configured to couple theinput signals to the amplifier, and to couple the input signals to thecapacitive touch controller via a high-pass filter.

The high pass filter may include a capacitance. The high-pass filter maybe a capacitance.

The device may include a plurality of amplifiers. Each amplifier may beconfigured for coupling to a first electrode of the touch panel. Thedevice may also include a multiplexer having an input coupled to theoutput of each amplifier, and an output coupled to an input of theanalog-to-digital converter.

The device may also include a multiplexer having a plurality of inputs,each input for coupling to a first electrode of the touch panel, and anoutput coupled to an input of the amplifier.

Apparatus may include the device and a touch panel including a layer ofpiezoelectric material disposed between a plurality of first electrodesand at least one second electrode.

A portable telecommunications device may include the device or theapparatus.

According to a second aspect of the invention there is provided a methodof processing signals from a projected capacitance touch panel, thetouch panel comprising a layer of piezoelectric material disposedbetween a plurality of first electrodes and at least one secondelectrode. The method includes, in response to receiving input signalsfrom a given first electrode, generating a capacitance signal indicativeof a capacitance of the given first electrode. The method also includes,in response to receiving input signals from a given first electrode,generating an amplified signal based on the input signal. The methodalso includes, in response to receiving input signals from a given firstelectrode, generating, using an analog-to-digital converter synchronisedwith the capacitance signal, a pressure signal indicative of a pressureapplied to the touch panel proximate to the given first electrode. Thepressure signal is generated by sampling the amplified signal at timescorresponding to the amplitude of the capacitance signal beingsubstantially equal to a ground, common mode or minimum value.

The times for sampling the amplified signal may correspond to thecapacitance signal being within ±100 μv, within ±1 mV, within ±2 mV,within ±5 mV, within ±10 mV, within ±20 mV, within ±50 mV or within ±100mV of a ground, common mode or minimum value of the capacitance signal.

The method may also include driving an electrode of the touch panelusing a capacitance measurement signal, such that the input signalsreceived from a given first electrode vary in dependence upon acapacitive coupling between the given first electrode and thecapacitance measurement signal, and in dependence upon a strain of thelayer of piezoelectric material proximate to the given first electrode.

The capacitance measurement signal may be for measuring aself-capacitance of a given first electrode. The capacitance measurementsignal may be for measuring a mutual capacitance between the given firstelectrode and another electrode.

The method may also include generating a synchronisation signal independence upon the capacitance measurement signal. The method may alsoinclude controlling the analog-to-digital converter to sample theamplified signal in dependence upon the synchronisation signal.

The synchronisation signal may be generated including an offset withrespect to the capacitance measurement signal. The offset may bedetermined in dependence upon a phase difference between the capacitancemeasurement signal and the input signals received from the firstelectrode.

Generating the capacitance signal may include generating, using a secondanalog-to-digital convertor, a digitised amplified signal by samplingthe amplified signal.

Generating the capacitance signal may include generating, using acontroller, the capacitance signal based on the digitised amplifiedsignal.

The method may also include sequentially generating the pressure signaland a digitised amplified signal. The pressure signal may be generatedby using the analog-to-digital converter to sample the amplified signalat a first sampling frequency, f_(piezo). The amplified signal may begenerated by using the analog-to-digital converter to sample theamplified signal at a second sampling frequency, f_(cap), which isgreater than the first sampling frequency. The method may also includegenerating, using a controller, the capacitance signal based on thedigitised amplified signal.

The controller may be configured to generate the capacitance signal byapplying a high pass filter to the digitised amplified signal.

According to a third aspect of the invention, there is provided a devicefor processing signals from a projected capacitance touch panel. Theprojected capacitance touch panel includes a layer of piezoelectricmaterial disposed between a number of sensing electrodes and at leastone counter electrode. The device includes a capacitive touch controllerhaving a number of measurement ports. The device also includes a numberof charge amplifiers. The device also includes a number of terminals forconnection to the sensing electrodes of the projected capacitance touchpanel. Each terminal is connected to one of the measurement ports. Eachterminal is also connected to an input of one of the charge amplifiersvia a corresponding switch of a number of switches. The device alsoincludes a controller configured to synchronise the capacitive touchcontroller and the number of switches so that during a first portion ofa cycle the capacitive touch controller outputs a capacitancemeasurement signal to one or more of the terminals, and the number ofcharge amplifiers are disconnected from the terminals by the respectiveswitches. The controller is also configured to synchronise thecapacitive touch controller and the number of switches so that during asecond portion of the cycle the capacitive touch controller does notoutput the capacitance measurement signal, and one or more of the chargeamplifiers are connected to the corresponding terminals by therespective switches.

During the second portion of the cycle, each of the charge amplifiersmay be connected to the corresponding terminal by the respective switch.

Each charge amplifier may be an integrating amplifier. Each integratingamplifier which is connected by a respective switch to a correspondingterminal may be reset one or more times during the second portion of thecycle.

The capacitive touch controller may be configured to measure capacitancevalues when the device is connected to the projected capacitance touchpanel.

The controller may be configured to measure force signals based onoutputs from the charge amplifiers when the device is connected to theprojected capacitance touch panel.

A system may include the device and a projected capacitance touch panelcomprising a layer of piezoelectric material disposed between a numberof sensing electrodes and at least one second electrode. Each sensingelectrode of the touch panel may be connected to a correspondingterminal of the device.

The number of sensing electrodes may include a number of first sensingelectrodes. Each first sensing electrode may extend in a first directionand the number of first sensing electrodes may be spaced apart in asecond direction. The second direction may be different to the firstdirection. The number of sensing electrodes may include a number ofsecond sensing electrodes. Each second sensing electrode may extend inthe second direction and the number of second sensing electrodes may bespaced apart in the first direction. The first and second sensingelectrodes may be electrically insulated from one another.

The number of sensing electrodes may include, or take the form of, anumber of sensing pads disposed to form an array.

According to a fourth aspect of the invention, there is provided adevice for processing signals from a projected capacitance touch panel.The projected capacitance touch panel includes a layer of piezoelectricmaterial disposed between a number of sensing electrodes and at leastone counter electrode. The device includes a controller having a numberof measurement ports. The controller is configured to output acapacitance measurement signal via one or more of the measurement ports.The device also includes a number of charge amplifiers. The device alsoincludes a number of terminals for connection to the sensing electrodesof the projected capacitance touch panel. Each terminal is connected toone of the measurement ports. Each terminal is also connected to one ofthe charge amplifiers via a corresponding switch of a number ofswitches. The controller is further configured to synchronise the numberof switches with the output of the capacitance measurement signal sothat during a first portion of a cycle the controller outputs acapacitance measurement signal to one or more terminals, and the numberof charge amplifiers are disconnected from the corresponding terminalsby the respective switches. The controller is further configured tosynchronise the number of switches with the output of the capacitancemeasurement signal so that during a second portion of the cycle thecontroller does not output the capacitance measurement signal, and oneor more of the charge amplifiers are connected to the correspondingterminals by the respective switches.

During the second portion of the cycle, each of the charge amplifiersmay be connected to the corresponding terminal by the respective switch.

Each charge amplifier may be an integrating amplifier. Each integratingamplifier which is connected by a respective switch to a correspondingterminal may be reset one or more times during the second portion of thecycle.

The controller may also be configured to measure capacitance valuesusing the capacitance measurement signal when the device is connected tothe projected capacitance touch panel.

The controller may also be configured to measure force signals based onoutputs from the charge amplifiers when the device is connected to theprojected capacitance touch panel.

A system may include the device and a projected capacitance touch panelcomprising a layer of piezoelectric material disposed between a numberof sensing electrodes and at least one second electrode. Each sensingelectrode of the touch panel may be connected to a correspondingterminal of the device.

The number of sensing electrodes may include a number of first sensingelectrodes. Each first sensing electrode may extend in a first directionand the number of first sensing electrodes may be spaced apart in asecond direction. The second direction may be different to the firstdirection. The number of sensing electrodes may include a number ofsecond sensing electrodes. Each second sensing electrode may extend inthe second direction and the number of second sensing electrodes may bespaced apart in the first direction. The first and second sensingelectrodes may be electrically insulated from one another.

The number of sensing electrodes may include, or take the form of, anumber of sensing pads disposed to form an array.

According to a fifth aspect of the invention, there is provided a methodemploying a projected capacitance touch panel. The projected capacitancetouch panel includes a layer of piezoelectric material disposed betweena number of sensing electrodes and at least one counter electrode. Themethod includes applying a capacitance measurement signal to one or moreof the sensing electrodes during a first portion of a cycle. The methodalso includes causing a number of switches to be open during the firstportion of the cycle. Each of the switches connects one of the sensingelectrodes to a corresponding charge amplifier. The method also includesstopping application of the capacitance measurement signal during asecond portion of the cycle. The method also includes connecting one ormore of the sensing electrodes to the corresponding charge amplifiersduring the second portion of the cycle, using the respective switches.

Each charge amplifier may be an integrating amplifier. The method mayalso include resetting each integrating amplifier one or more timesduring the second portion of the cycle.

The method may also include measuring one or more capacitance valuesbased on the capacitance measurement signal during the first portion ofthe cycle.

The method my also include measuring force signals based on outputs fromthe charge amplifiers during the second portion of the cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings in which:

FIG. 1 illustrates a first apparatus for combined capacitive andpressure sensing;

FIG. 2 illustrates a second apparatus for combined capacitive andpressure sensing;

FIG. 3 illustrates an electronic device incorporating a touch panel;

FIG. 4 illustrates separation of a single signal into pressure andcapacitance signals;

FIG. 5 illustrates a first touch panel system;

FIGS. 6A to 6C illustrate using synchronised sampling to obtain apressure signal;

FIG. 7 is a circuit diagram for an example of charge amplifiers for usein the first touch panel system;

FIG. 8 illustrates a second touch panel system;

FIG. 9 is a circuit diagram for an example of charge amplifiers for usein the second touch panel system;

FIG. 10 illustrates a third touch panel system;

FIG. 11 is a plan view of an alternative electrode layout;

FIG. 12 is a plan view of a third touch panel;

FIG. 13 is a plan view of a patterned electrode;

FIG. 14 is a plan view of a fourth touch panel;

FIG. 15 is a cross-sectional view of a fourth touch panel;

FIG. 16 illustrates a third apparatus for combined capacitive andpressure sensing;

FIG. 17 illustrates a fifth touch panel system;

FIG. 18 is a circuit diagram for an example of a charge amplifier foruse in the fifth touch panel system;

FIG. 19 illustrates a sixth touch panel system;

FIG. 20 is a circuit diagram for an example of a charge amplifier foruse in the sixth touch panel system;

FIG. 21 is a cross-sectional view of a first display stack-up;

FIG. 22 is a cross-sectional view of a second display stack-up;

FIG. 23 is a cross-sectional view of a first embedded stack-up;

FIG. 24 is a cross-sectional view of a second embedded stack-up;

FIG. 25 illustrates a seventh touch panel system;

FIG. 26 illustrates synchronisation of capacitance and force sensing forthe seventh touch panel system;

FIG. 27 is a circuit diagram for an example of a charge amplifier foruse in the seventh touch panel system;

FIG. 28 illustrates an eighth touch panel system;

FIG. 29 illustrates a ninth touch panel system;

FIG. 30 illustrates a tenth touch panel system; and

FIG. 31 is a circuit diagram for an example of a charge amplifier foruse in the tenth touch panel system.

DETAILED DESCRIPTION

In the following description, like parts are denoted by like referencenumerals.

First Combined Capacitance and Pressure Sensing Apparatus and FirstTouch Sensor.

FIG. 1 schematically illustrates a first apparatus 1 for combinedcapacitive and pressure sensing which includes a first touch sensor 2, afront end module 3 and a controller 19.

The first touch sensor 2 includes a layer structure 4 having a firstface 5 and a second, opposite, face 6, a first electrode 7 and a secondelectrode 8. The layer structure 4 includes one or more layers,including at least a layer of piezoelectric material 9. Each layerincluded in the layer structure 4 is generally planar and extends infirst x and second y directions which are perpendicular to a thicknessdirection z. The one or more layers of the layer structure 4 arearranged between the first and second faces 5, 6 such that the thicknessdirection z of each layer of the layer structure 4 is perpendicular tothe first and second faces 5, 6. The first electrode 7 is disposed onthe first face 5 of the layer structure 4, and the second electrode 8 isdisposed on the second face 6 of the layer structure 4 The firstelectrode 7 is electrical coupled to a terminal A and the secondelectrode 8 is coupled to a terminal B.

Preferably, the layer of piezoelectric material 9 is a piezoelectricpolymer such as polyvinylidene fluoride (PVDF) or polylactic acid.However, the piezoelectric material may alternatively be a layer of apiezoelectric ceramic such as lead zirconate titanate (PZT). Preferably,the first and second electrodes 7, 8 are indium tin oxide (ITO) orindium zinc oxide (IZO). However, the first and second electrodes 7, 8may be metal films such as aluminium, copper, silver or other metalssuitable for deposition and patterning as a thin film. The first andsecond electrodes 7, 8 may be conductive polymers such as polyaniline,polythiphene, polypyrrole or poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT/PSS). The first and second electrodes 7, 8may be formed from a metal mesh; nanowires, optionally silver nanowires;graphene; and carbon nanotubes.

The front end module 3 is coupled to the first touch sensor 2 viaterminal A in order to receive an input signal 10 from the firstelectrode 7. The front end module 3 includes a first stage 11 in theform of an amplification stage, and a second stage in the form of afirst frequency-dependent filter 12 and a second frequency-dependentfilter 13. The first stage 11 receives the input signal to from thefirst electrode 7, and provides an amplified signal 14 based on theinput signal 10. The first frequency-dependent filter 12 receives andfilters the amplified signal 14 to provide a first filtered signal 15having a first frequency bandwidth. The second frequency-dependentfilter 13 receives and filters the amplified signal 14 to provide asecond filtered signal 16 having a second frequency bandwidth. Thesecond frequency bandwidth has a relatively larger upper-frequency thanthe first frequency bandwidth.

The first stage it may receive an alternating signal 17, V_(sig)(t)supplied by a signal source 18. The amplified signal 14 may be based onthe input signal 10 and the alternating signal 17. In general, thealternating signal 17 may be any alternating signal which is suitablefor use in determining the self-capacitance or mutual capacitance of anelectrode of a projected capacitance touch panel.

The first apparatus may be configured to drive the first or secondelectrode 7, 8 of the touch sensor 2 using the alternating signal 17,V_(sig)(t) as a capacitance measurement signal, such that the inputsignals 10 received from the first electrode 7 vary in dependence upon acapacitive coupling between the first and/or second electrodes 7, 8 andthe alternating signal 17, V_(sig)(t), and in dependence upon a strainof the layer of piezoelectric material 9.

The first and second frequency dependent filters 12, 13 may be hardwarefilters such as, for example, active or passive filtering circuits.Alternatively, the amplified signal 14 may be converted into a digitalsignal by an analog-to-digital converter (ADC) and the first and secondfrequency dependent filters 12, 13 may be implemented in the digitaldomain using, for example, one or more microprocessors,microcontrollers, field programmable gate arrays or other suitable dataprocessing devices. Thus, in some examples, the first and secondfrequency dependent filters 12, 13 may not form part of the analog frontend 3, and may instead be implemented by the controller 19.Implementation of the first and second frequency dependent filters 12,13 of the second stage in hardware or in the digital domain have beendescribed in WO 2016/102975 A2.

The present application is primarily concerned with an implementation ofthe first and second frequency dependent filters 12, 13 based on usingone or more analog-to-digital converters (ADC) 500 (FIG. 5) to samplethe amplified signal 14 at a first, relatively low sampling frequency,f_(piezo), and at a second, relatively high sampling frequency, f_(cap).In effect, sampling by an analog-to-digital converter includes afrequency filtering effect as a consequence of the Nyquist criterion.The present invention is based, at least in part, on the realisationthat the first filtered signal 15 corresponding to the piezoelectricresponse to an applied pressure may be extracted from the combinedamplified signal 14 by using an ADC 50 (FIG. 5) synchronised to lowlevel or off periods of the alternating signal 17, V_(sig)(t) used tomeasure capacitance. In other words, the first filtered signal 15, whichis a signal indicative of an applied pressure, may be obtained bysampling the amplified signal 14 at times corresponding to the amplitudeof the alternating signal 17, V_(sig)(t) being substantially equal to aground, common mode or minimum value. The second filtered signal 16representing the capacitance may be obtained by sampling at a higherfrequency f_(cap), followed by filtering in the digital domain by thecontroller 19 to remove low frequency components. For example, thecontroller 19 may apply a high pass filter. An alternative approach isto treat the signal due to the piezoelectric response as a slowlyvarying baseline—for example, the most recently obtained sample of thefirst filtered signal 15 may be stored and used as a DC offset forcorrecting samples of the second filtered signal 16 obtained at thehigher sampling frequency f_(cap).

In the present specification, the pressure signal filter 12 maytherefore take the form of an ADC 50 (FIG. 5) which is a part of thefront end 3, or which is integral with the controller 19. Similarly, thecapacitance signal filter 13 may be a part of the front end 3, may beimplemented by the controller 19, or the capacitance signal filter 13may be implemented by the front end 3 and the controller 19 incombination.

The input signal to is produced in response to a user interaction withthe touch sensor 2, or with a layer of material overlying the touchsensor 2. In the following description, reference to a “userinteraction” shall be taken to include a user touching or pressing atouch sensor, a touch panel or a layer of material overlying either. Theterm “user interaction” shall be taken to include interactions involvinga user's digit or a stylus (whether conductive or not). The term “userinteraction” shall also be taken to include a user's digit or conductivestylus being proximate to a touch sensor or touch panel without directphysical contact.

The terminal B may couple the second electrode 8 to ground, to a commonmode voltage V_(CM), to a signal source 18 providing an alternatingsignal 17, V_(sig)(t) or to another front end module 3 (not shown inFIG. 1). Alternatively, the terminal B may be connected to the samefront end module 3, such that the front end module 3 is connected acrossthe terminals A and B.

The terminals A, B, and other terminals denoted herein by capitalisedLatin letters are used as reference points for describing electricalcoupling between electrodes and other elements of an apparatus. Althoughthe terminals A, B may actually be physical terminals, the descriptionthat an element, for example a front end module 3, is coupled to aterminal, for example, the terminal A, shall be taken to also encompassthe possibility that the front end module may be directly coupled to thefirst electrode 8. Similarly for other elements and other terminalsdenoted by capitalised Latin letters.

The controller 19 receives the first and second filtered signals 15, 16.In some examples, the controller 19 may also serve as the signal source18 providing an alternating signal 17, V_(sig)(t). The controller 19calculates pressure values 20 based on the first filtered signal 15 andcapacitance values 21 based on the second filtered signal 16. Thepressure values 20 depend upon a deformation, which may be a strain,applied to the layer of piezoelectric material 9 and corresponding to auser interaction. The capacitance values 21 depend upon theself-capacitance of the first electrode 7 and/or a mutual capacitancebetween the first and second electrodes 7, 8. The capacitance values 22vary in response to a user interaction involving a digit or a conductivestylus.

In this way, pressure and capacitance measurements may be performedusing the touch sensor 2 without the need for separate pressure andcapacitance electrodes. A single input signal to is received from thefirst electrode 7 which includes pressure and capacitance information.Additionally, the input signal to may be amplified and processed using asingle front end module 3. This can allow the apparatus 1 to be morereadily integrated into existing projected capacitance touch panels. Thelayer structure 4 may include only the layer of piezoelectric material 9such that the first and second opposite faces 5, 6 are faces of thepiezoelectric material layer 9. Alternatively, the layer structure 4 mayinclude one or more dielectric layers which are stacked between thelayer of piezoelectric material 9 and the first face 5 of the layerstructure 4. The layer structure 4 may include one or more dielectriclayers stacked between the second face 6 of the layer structure 4 andthe layer of piezoelectric material 9. Preferably, one or moredielectric layer(s) include layers of a polymer dielectric material suchas polyethylene terephthalate (PET), or layers of pressure sensitiveadhesive (PSA) material. However, one or more dielectric layer(s) mayinclude layers of a ceramic insulating material such as aluminium oxide.

In FIG. 1, the first and second faces 5, 6 and the layers of the layerstructure 4 are shown extending along orthogonal axes labelled x and y,and the thickness direction of each layer of the layer structure 4 isaligned with an axis labelled z which is orthogonal to the x and y axes.However, the first, second and thickness directions need not form aright handed orthogonal set as shown. For example, the first and seconddirections x, y may intersect at an angle of 30 degrees or 45 degrees orany other angle greater than 0 degrees and less than 90 degrees.

Second Combined Capacitance and Pressure Sensing Apparatus and SecondTouch Sensor:

Referring also to FIG. 2, a second apparatus 22 is shown which includesa second touch sensor 23, a first front end module 3 a, a second frontend module 3 b and a controller 19.

The second touch sensor 23 is similar to the first touch sensor 2,except that the second touch sensor 23 also includes a second layerstructure 24 having a third face 25 and a fourth, opposite, face 26, anda third electrode 27. The second layer structure 24 includes one or moredielectric layers 28. Each dielectric layer 28 is generally planar andextends in first x and second y directions which are perpendicular to athickness direction z. The one or more dielectric layers 28 of thesecond layer structure 24 are arranged between the third and fourthfaces 25, 26 such that the thickness direction z of each dielectriclayer 28 of the second layer structure 24 is perpendicular to the thirdand fourth faces 25, 26. The third electrode 27 is disposed on the thirdface 25 of the second layer structure 24, and the fourth face 26 of thesecond layer structure 24 contacts the first electrode 7.

Preferably, the dielectric layer(s) 28 include layers of a polymerdielectric material such as PET or layers of PSA materials. However, thedielectric layer(s) 28 may include layers of a ceramic insulatingmaterial such as aluminium oxide. Preferably, the third electrode 27 ismade of indium tin oxide (ITO) or indium zinc oxide (IZO). However, thethird electrode 27 may be a metal mesh film such as aluminium, copper,silver or other metals suitable for deposition and patterning as a thinfilm. The third electrode 27 may be made of a conductive polymer such aspolyaniline, polythiphene, polypyrrole orpoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS).

The first and second front end modules 3 a, 3 b are the same as thefront end module 3. The first front end module 3 a is coupled to thesecond touch sensor 23 via a terminal D in order to receive a firstinput signal 10 a from the first electrode 7. The second front endmodule 3 b is coupled to the second touch sensor 23 via a terminal C inorder to receive a second input signal 10 b from the third electrode 27.A terminal E may couple the second electrode 8 to ground, to a commonmode voltage V_(CM), or to a signal source 18 providing an alternatingsignal 17, V_(sig)(t). Alternatively, the terminal E may be coupled tothe first front end module 3 a such that the first front end module 3 ais connected across the terminals D and E, and the terminal E may alsobe coupled to the second front end module 3 b such that the second frontend module 3 b is connected across the terminals C and E. One or both ofthe first and second front end modules 3 a, 3 b may be connected to asignal source 18 in order that the corresponding first stage(s) 11 mayreceive an alternating signal 17, V_(sig)(t).

The controller 19 receives first and second filtered signals 15 a, 16 afrom the first front end module 3 a and first and second filteredsignals 15 b, i 6 b from the second front end module 3 b. The controller19 calculates first pressure values 20 a based on the first filteredsignal 15 a from the first front end module 3 a and second pressurevalues 20 b based on the first filtered signal 15 b from the secondfront end module 3 b. The content of pressure values 21 depends on ameasurement mode of the controller 19. The controller 19 may be operablein a self-capacitance measurement mode or a mutual capacitancemeasurement mode, and may be switchable between measurement modes. Whenself-capacitances of the first and third electrodes 7, 27 are measured,the controller 19 calculates self-capacitance values for the firstelectrode 7 based on the second filtered signal 16 a from the firstfront end module 3 a and self-capacitance values for the third electrode27 based on the second filtered signal 16 b from the second front endmodule 3 b. When a mutual capacitance between the first and thirdelectrodes 7, 27 is measured, the controller 19 calculates the mutualcapacitance based on the second filtered signals 16 a, 16 b from bothfirst and second front end modules 3 a, 3 b.

The pressure values 20 a, 20 b depend upon a deformation applied to thelayer of piezoelectric material 9 by a user interaction. The capacitancevalues 21 may include self-capacitances of the first and thirdelectrodes 7, 27, or a mutual capacitance measured between the first andthird electrodes 7, 27, depending on the operation mode of thecontroller 19. The capacitance values 21 vary in response to a userinteraction involving a digit or a conductive stylus.

The second layer structure 24 may include only a single dielectric layer28, such that the third and fourth opposite faces 25, 26 are faces of asingle dielectric layer 28. Alternatively, a second layer structure 24need not be used, and the third electrode 27 may be disposed on thefirst face 5 along with the first electrode 7. In FIG. 2, the third andfourth faces 25, 26 and the dielectric layers 28 of the second layerstructure 24 are shown extending along orthogonal axes labelled x and y,and the thickness direction of each dielectric layer 28 of the secondlayer structure 24 is aligned with an axis labelled z which isorthogonal to the x and y axes. However, the first, second and thicknessdirections need not form a right handed orthogonal set as shown.

Electronic Device:

Referring also to FIG. 3, an electronic device 29 may include a touchpanel 30 and a touch controller 31 for providing combined capacitive andpressure sensing.

The electronic device 29 may be a relatively immobile electronic devicesuch as, for example a desktop computer, an automated teller machine(ATM), a vending machine, a point of sale device, or a public accessinformation terminal. Alternatively, an electronic device 29 may be aportable electronic device such as a laptop, notebook or tabletcomputer, a mobile phone, a smart phone, a personal data assistant or amusic playing device. The electronic device 29 includes a touch panel 30including one or more touch sensors 2, 23. The touch panel 30 is coupledto a touch controller 31 including, for example, one or more front endmodules 3 by a link 32. In a case where the link 32 is a multiplexedlink, one front end module 3 may receive input signals to from multipletouch sensors 2, 23. For example, using a multiplexed link 32 the touchcontroller 31 may include one front end module and the touch panel 30may include two, four, eight, sixteen, thirty two, sixty four, onehundred and twenty eight, two hundred and fifty six or more touchsensors 2, 23. The number of touch sensors 2, 23 coupled to a front endmodule 3 by a multiplexed link 32 need not be a power of two.

The electronic device 29 may include a processor 33 for executingprograms and processing information. The electronic device 29 mayinclude a memory 34 such as a volatile random access memory fortemporarily storing programs and information, and/or storage 35 such asnon-volatile random access memory (NVRAM) or a hard disc drive (HDD) forlong term storage of programs and information. The electronic device 29may include a network interface 36 for transmitting and/or receivinginformation from wired or wireless communication networks. Theelectronic device 29 may include a removable storage interface 37 whichcan interface with removable storage media to read and/or write programsand information. The electronic device 29 may include output means suchas a display 38 and/or speaker(s) 39. The display 38 may be any type ofdisplay such as, for example, an liquid crystal display (LCD), a lightemitting diode display (LED), an organic LED display, an electrophoreticdisplay or other type of electronic-ink display.

The touch controller 31 provides input information to the electronicdevice 29 which corresponds to user interactions with the touch panel30. For example, input information may be the locations and/or pressuresof one or more user interactions. The electronic device may includeother input means such as a microphone 40, or other input devices 41such as, for example, a keyboard, keypad, mouse or trackball. When thetouch panel 30 includes a plurality of touch sensors 2, 23, the touchcontroller 31 may provide positional information in the form ofcoordinates and/or pressures corresponding to one user interaction ortwo or more simultaneous user interactions with the touch panel 30.

The touch panel 30 may be provided overlying the display 38, such thatthe touch panel 30 and display 38 provide a touch screen. Alternatively,the touch sensors 2, 23 of the touch panel 30 may be integrated into orembedded within the display 38. When the touch panel 30 is usedoverlying or integrated into the display 38, the layer structure(s) 4,24 and electrodes 7, 8, 27 may be transparent or substantiallytransparent. For example, the layer structure(s) 4, 24 and electrodes 7,8, 27 may transmit 50% or more, preferably at least 75%, preferably atleast 90% of light in visible wavelengths. For example, thepiezoelectric material may be PVDF, dielectric layers included in thelayers structures 4, 24 may be PET or an optically transparent orsubstantially transparent PSA, and the electrodes 7, 8, 27 may be ITO.Alternatively, the electrodes 7, 8, 27, and any connections thereto, maybe opaque and sufficiently thin in a direction perpendicular to thethickness direction z that they are not immediately noticeable to thehuman eye, for example, electrodes, and any connections thereto, may beformed of mesh having tracks less than 100 micrometers (1×10⁻⁴ m) wide,less than to micrometers (1×10⁻⁵ m) wide or thinner.

Operation of the First and Second Apparatuses:

Referring also to FIG. 4, separation of pressure and capacitance signalswill be explained.

The layer of piezoelectric material 9 is poled such that a polarisationP of the layer of piezoelectric material 9 will be generated by theapplication of a pressure (or stress or force) applied in the thicknessdirection z which results from a user interaction with the touch sensor2, 23. The polarisation P of the layer of piezoelectric material resultsin an induced electric field E_(p), which has a component E_(c) in thethickness direction. The deformation which produces the polarisation Pmay result from a compression or a tension. The deformation whichproduces the polarisation P may include an in-plane stretching of thepiezoelectric material layer 9 in response to the applied pressure.

The induced electric field E_(p) produces a potential difference betweenthe first and second electrodes 7, 8 of the first or second touchsensors 2, 23. The induced electric field E_(p) produces a potentialdifference between the third and second electrodes 27, 8 of the secondtouch sensor 23. If a conductive path is provided between the first orthird electrodes 7, 27 and the second electrode 8, charges will flowbetween them until the induced electric field E_(p) is cancelled by anelectric field E_(q) produced by the charging of the electrodes 7, 8,27. Intimate contact between the layer of piezoelectric material 9 andthe electrodes 7, 8, 27 is not required, provided that interveninglayers of the layer structures 4, 24 are not excessively thick. Apotential difference may be produced between the third and secondelectrodes 27, 8 of the second touch sensor 23 provided that the firstelectrode 7 is arranged such that the third electrode 27 is not entirelyscreened from the induced electric field E_(p).

The input signal 10 received from the first electrode 7 or the thirdelectrode 27 includes a current signal I_(piezo)(t) which depends uponthe induced electric field E_(p). Generally, a greater deformationapplied to the layer of piezoelectric material 9 will result in agreater magnitude of I_(piezo)(t). The first stage 11 includes a circuitproviding an integrating amplifier which integrates the current signalI_(piezo)(t) and multiplies by a gain G in order to provide anintegrated output voltage signal V_(piezo)(t). The gain G need not befixed, and in general may be by a function of time, frequency and/or theelectrical parameters of a feedback network included in the first stage11.

The amplified signal 14 is approximately a superposition of theintegrated output voltage signal V_(piezo)(t) and a capacitancemeasurement voltage signal V_(cap)(t). The capacitance voltage signalV_(cap)(t) is an alternating signal having a basic frequency of f_(d).The capacitance voltage signal V_(cap)(t) is based on the capacitance ofthe touch sensor 2, 23 and an alternating signal 17, V_(sig)(t) providedby a signal source 18.

For the first touch sensor 2, a signal source 18 may be coupled to thefront end module 3 or to the second electrode 8 via terminal B. For thesecond touch sensor 23, signal source(s) 18 may be coupled to one orboth of the first and second front end modules 3 a, 3 b, or to thesecond electrode 8 via terminal E. The signal source 18 may be a voltagecontrolled source. The signal source 18 may be the controller 19, or adriving output of a separate projected capacitive touch controller.

The signal source 18 may provide an alternating signal 17, V_(sig)(t)having a sinusoidal, square, triangular or saw-toothed waveform. Thesignal source 18 may provide a periodic signal comprising asuperposition of two or more sinusoidal waveforms having differentfrequencies. The alternating signal 17, V_(sig)(t) may be any signalsuitable for measuring the self-capacitance or mutual capacitance of anelectrode of a projected capacitance touch panel. Preferably, thealternating signal 17, V_(sig)(t) is a pulsed or stepped signal formeasuring the self-capacitance of an electrode or the mutual capacitancebetween a pair of electrodes.

Preferably, the front end module 3 receives the alternating signal 17,V_(sig)(t) and the first stage 11 provides the amplified signal 14 basedon the input signal to and the alternating signal 17, V_(sig)(t). Anelectrode 7, 8 of the touch sensor 2 is driven using the alternatingsignal 17, V_(sig)(t) as a capacitance measurement signal. For example,the second electrode 8 may be driven at the alternating signal 17,V_(sig)(t). Alternatively, the second electrode 8 may be held at aground or common mode potential and the first electrode 7 may be drivenby the inverting input of an operational amplifier forming part of thefirst stage 11, by supplying the alternating signal 17, V_(sig)(t) tothe corresponding non-inverting input. In either approach, input signalsto received from the first electrode to may be caused to vary independence upon a capacitive coupling between the first electrode 7 andthe alternating signal 17, V_(sig)(t), and in dependence upon a strainof the layer of piezoelectric material 9 proximate.

The amplified signal 14 is approximately a superposition of theintegrated output voltage signal V_(piezo)(t) and the capacitancemeasurement voltage signal V_(cap)(t). However, the integrated outputvoltage signal V_(piezo)(t) and the capacitance measurement voltagesignal V_(cap)(t) generally have different frequency contents. Thesedifferent frequency contents facilitate separation using the first andsecond frequency-dependent filters 12, 13 or, in the presentspecification, using one or more ADCs 50, 51 (FIG. 5) operating at firstand second sampling frequencies f_(piezo), f_(cap). Where a userinteraction does not apply a pressure to the layer of piezoelectricmaterial 9 the contribution of the integrated output voltage signalV_(piezo)(t) to the amplified signal 14 may be zero or negligible.

Self capacitances of the first or third electrodes 7, 27, or mutualcapacitances between any pair of the first, second or third electrodes7, 8, 27 may typically fall within the range of 0.1 to 3000 pF or more,and preferably 100 to 2500 pF. In order to effectively couple tocapacitances in this range, the alternating signal 17, V_(sig)(t) maytypically have a base frequency of greater than or equal to 10 kHz,greater than or equal to 20 kHz, greater than or equal to 50 kHz orgreater than or equal to too kHz.

By contrast, the integrated output voltage signal V_(piezo)(t) typicallyincludes a broadband frequency content spanning a range from several Hzto several hundreds or thousands of Hz. This is at least in part becausethe integrated output voltage signal V_(piezo)(t) arises from userinteractions by a human user.

Preferably, the first frequency-dependent filter 12 attenuates thecapacitance measurement voltage signal V_(cap)(t) such that the firstfiltered signal 15 is not based on the alternating signal 17,V_(sig)(t). Preferably, the first filtered signal 15 is substantiallyequal to the integrated output voltage signal V_(piezo)(t), or at leastis primarily based on the piezoelectric current I_(piezo)(t). In thepresent specification, the first frequency-dependent filter 12 isimplemented using an ADC 50 (FIG. 5) synchronised to sample the firstfiltered signal 15 at times corresponding to the amplitude of thealternating signal 17, V_(sig)(t) and capacitance measurement voltagesignal V_(cap)(t) being substantially equal to a ground, common mode orminimum value.

The first filtered signal 15 is generated by sampling the amplifiedsignal 14 at times corresponding to the amplitude of the alternatingsignal 17, V_(sig)(t) being substantially equal to a ground, common modeor minimum value. For example, if the alternating signal 17, V_(sig)(t)is a to kHz pulsed wave alternating between an off state of 0 V and anon state of V_(pulse), then the first frequency f_(piezo) would be tokHz with sampling times synchronised to the periods when V_(sig)(t)=0 V,i.e. during minima of the capacitance measurement signals. The value of0 V is merely an example, and in other examples a different referencevoltage level may be used such as, for example, a ground or common modepotential of a device incorporating the apparatus 1, 22. By contrast,the second frequency f_(cap) would need to be a multiple of at leastseveral times 10 kHz in order to capture sufficient details to determinea capacitance value.

In some examples, the synchronisation may need to take account of aphase shift between the alternating signal 17, V_(sig)(t) andcapacitance measurement voltage signal V_(cap)(t). For example, byadjusting the duration of a period of ground, common mode or minimumsignal level of the alternating signal 17, V_(sig)(t) such that there isoverlap with a period of ground, common mode or minimum signal level ofthe capacitance measurement voltage signal V_(cap)(t) within an expectedor calibrated range of capacitance values. The capacitance measurementvoltage signal V_(cap)(t) may be a transmitted or driving signal, or maybe a received signal.

Preferably, the second frequency-dependent filter 13 selects thecapacitance measurement voltage signal V_(cap)(t) such that the secondfiltered signal 16 is based on the alternating signal 17, V_(sig)(t) andthe capacitance of the touch sensor 2, 23. Preferably, the secondfiltered signal 16 is substantially equal to the capacitance measurementvoltage signal V_(cap)(t), or is at least primarily based on thealternating signal 17, V_(sig)(t). In the present specification, thesecond frequency-dependent filter 13 may be implemented in the digitaldomain following initial sampling of the amplified signal 14 at thesecond sampling frequency f_(cap). For example, the controller 19 mayimplement the second frequency-dependent filter 13 by applying ahigh-pass filter. Alternatively, since the integrated output voltagesignal V_(piezo)(t) varies at frequencies several orders of magnitudebelow typical capacitance measurement signals V_(cap)(t), the mostrecent sample or samples from the first filtered signal 15 may be usedas a flat or interpolated baseline for subtraction from the sampledvalues of the amplified signal 14 to obtain the second filtered signal16.

Further details of the implementation of the first and second frequencydependent filters 12, 13 are described hereinafter with reference toFIGS. 6A to 6C.

In this way, the amplitude of the first filtered signal 15 is dependentupon a pressure applied to the layer of piezoelectric material 9 by auser interaction, and the amplitude of the second filtered signal 16 isdependent upon a capacitance of the touch sensor 2, 23 as modified bythe proximity of a user's digit or conductive stylus.

The first stage 11 has a frequency response having a low frequencycut-off f_(l) and a high frequency cut-off f_(u). Below the lowfrequency cut-off f_(l) and above the high frequency cut-off f_(u) thegain G of the first stage 11 drops rapidly so that frequencies outsidethe range between f_(l) and f_(u) are blocked. The high frequencycut-off f_(u) is greater than the base frequency f_(d) of thealternating signal 17, V_(sig)(t) for capacitance measurements. Thelow-frequency cut-off f_(l) is preferably at least 1 hertz, or at leastsufficiently high to substantially block voltage signals resulting froma pyroelectric effect in the layer of piezoelectric material 9 whichresult from the body temperature of a user's digit. For application inan industrial or domestic environment, the low frequency cut-off f_(l)may be at least 50 Hz, at least 60 Hz or at least sufficiently high toreject noise pick-up at a frequency of a domestic of industrial powerdistribution network and resulting from ambient electric fields. The lowfrequency cut-off f_(l) may be at least 100 Hz. The low frequencycut-off f_(l) may be at least 200 Hz. For application in aircraft, thelow frequency cut-off f_(l) may be at least 400 Hz. Frequency cut-offsmay corresponds to 3 dB attenuation.

First Touch Panel System:

Touch panel systems including touch panels including multiple touchsensors 2, 23 combined with apparatus for combined capacitance andpressure sensing have been described in WO 2016/102975 A2, in particularwith reference to FIGS. 15 to 18, 21, and 25 to 29 of this document.

In the touch panel systems described in WO 2016/102975 A2, the first andsecond frequency dependent filters 12, 13 are implemented in hardware asa part of front end modules, or in the digital domain, for example by acontroller. By contrast, touch panel systems of the presentspecification implement the first frequency dependent filter 12 using ananalog-to-digital converter (ADC) 50 (FIG. 5) which is synchronised withthe alternating signal 17, V_(sig)(t) at a first sampling frequencyf_(piezo). Touch panel systems of the present specification implementthe second frequency dependent filter 13 in the digital domain. Forexample, by application of a digital high-pass filter, or by using themore recently sample value or values of the first filtered signal 15 asa correction for the underlying variation of the output signalV_(piezo)(t).

An advantage of the examples of the present specification, as comparedto the touch panel systems described in WO 2016/102975 A2, is thatobtaining the first filtered signal 15 using a synchronised ADC mayallow for a reduced hardware footprint as compared to a separate activeor passive hardware filter. This is because an ADC is required in anyevent for input to a controller or other data processing apparatus.Additionally, compared to implementing the first frequency dependentfilter 12 in the digital domain, obtaining the first filtered signal 15using a synchronised ADC reduces the data processing requirements of atouch panel system. Although the second frequency dependent filter 13 isstill implemented in the digital domain, isolating the second filteredsignal 16 from the amplified signal 14 is relatively more reliable thanisolating the first filtered signal 15, because the amplitude of thesecond filtered signal 16 is typically larger, or significantly larger,than the amplitude of the first filtered signal 15.

In the touch panel systems described in WO 2016/102975 A, each front endmodule 3 is connected to a number of electrodes using a multiplexer. Inother words, electrode input signals 10 are multiplexed beforeamplification. Such systems are simple in that large numbers of frontend modules 3 and first stages 11 are not required. In this way,multiplexing the electrode input signals 10 before amplification allowsthe size and complexity of an apparatus for connection to a touch panelto be minimised.

However, in addition to the advantages of obtaining the first filteredsignal 15 using a synchronised ADC, it has been surprisingly realisedthat, despite increasing the overall size and complexity of an apparatusfor combined capacitance and pressure sensing, multiplexing theamplified signals 14 instead of the input signals 10 may provideimproved performance, as described hereinafter.

Referring also to FIG. 5, a first touch panel system 42 includes a firsttouch panel 43 and a first touch controller 44 for combined pressure andcapacitance sensing.

The first touch panel 43 includes first and second layer structures 4,24 which are generally the same as the layer structures 4, 24 of thesecond touch sensor 23, except that multiple first electrodes 7 aredisposed on the first face 5 of the first layer structure 4 and thatmultiple third electrodes 27 are disposed on the third face 25 of thesecond layer structure 24.

The first electrodes 7 each extend in the second direction y and thefirst electrodes 7 are disposed in an array evenly spaced in the firstdirection x. The third electrodes 27 each extend in the first directionx and the third electrodes 27 are disposed in an array evenly spaced inthe second direction y. Each first electrode 7 and each third electrode27 is coupled to a corresponding conductive trace 45. The secondelectrode 8 is disposed on the second face 6 of the first layerstructure 4 and is extensive such that the second electrode 8 at leastpartially underlies each first electrode 7 and each third electrode 27.The second electrode 8 may be substantially coextensive with the secondface 6 of the first layer structure 4. The second electrode 8 isconnected to a common mode voltage V_(CM).

In this way, the area around each intersection of a first electrode 7with a third electrode 27 effectively provides a second touch sensor 23.

The first touch panel 43 may be bonded overlying the display 38 of anelectronic device 29. In this case, the materials of the first touchpanel 43 should be substantially transparent as described hereinbefore.A cover lens 46 (FIG. 21) may be bonded overlying the first touch panel43. The cover lens 46 (FIG. 21) is preferably glass but may be anytransparent material. The cover lens 46 (FIG. 21) may be bonded to thefirst touch panel 43 using a layer of pressure sensitive adhesive (PSA)material 109 (FIG. 22). The layer of PSA material 109 (FIG. 22) may besubstantially transparent. The first and third electrodes 7, 27 may befabricated using index matching techniques to minimise visibility to auser.

The first touch controller 44 includes a controller 47, a pair ofamplifier modules 48 a, 48 b a pair of multiplexers 49 a, 49 b, a pairof primary ADCs 50 a, 50 b and a pair of secondary ADCs 51 a, 51 b. Thecontroller 47 may communicate with the processor 33 of the electronicdevice 29 using a link 32. The controller 47 includes a signal source 18for providing the alternating signal 17, V_(sig)(t) to one or both ofthe amplifier modules 48 a, 48 b.

The amplifier modules 48 a, 48 b are similar to the first stage x,except that each amplifier module 48 a, 48 b includes a number ofseparate charge amplifiers 52. Each charge amplifier 52 of the firstamplifier module 48 a is connected to a corresponding third electrode 27via a respective terminal C1, . . . , C5 and conductive trace 45. Theoutput of each charge amplifier 52 of the first amplifier module 48 a isconnected to a corresponding input of the first multiplexer 49 a. Inthis way, the first multiplexer 49 a may output an amplified signal 14 acorresponding to an addressed third electrode 27.

The first primary ADC 50 a receives the amplified signal 14 acorresponding to a presently addressed third electrode 27 from the firstmultiplexer 49 a output. The first primary ADC 50 a also receives asynchronisation signal 53 from the controller 47 (also referred to as a“clock signal”). The synchronisation signal 53 triggers the firstprimary ADC 50 a to obtain samples at the first sampling frequencyf_(piezo) and at times corresponding to the amplitude of the alternatingsignal 17, V_(sig)(t) being substantially equal to a ground, common modeor minimum value. In this way, the first primary ADC 50 a may obtain thefirst filtered signal 15 a in the form of a sampled first filteredsignal 15 a which corresponds approximately to values of the integratedoutput voltage signal V_(piezo)(t) at the sampling times. Thesynchronisation signal 53 need not trigger the first primary ADC 50 a toobtain samples during every single period of the alternating signal 17,V_(sig)(t), and instead may trigger the first primary ADC 50 a to obtainsamples during, for example, every other period, every tenth period,every hundredth period and so forth.

For example, referring also to FIGS. 6A to 6C, an example of obtainingthe first filtered signal 15 a is illustrated. For visual purposes, inFIGS. 6A to 6C, the capacitance measurement voltage signal V_(cap)(t)and the integrated output voltage signal V_(piezo)(t) have beenillustrated with much smaller disparities in frequency and amplitudethan would be expected in practice. In practice, the capacitancemeasurement voltage signal V_(cap)(t) would be expected to have asignificantly larger amplitude and to vary at a frequency several ordersof magnitude larger than the integrated output voltage signalV_(piezo)(t).

Referring in particular to FIG. 6A, an example of the alternating signal17, V_(sig)(t) may have the form a pulsed wave with a 50:50 duty ratio,an amplitude of V_(a) and a period of 1/f_(d). In this example, thesynchronisation signal 53 triggers the first primary ADC 50 a atapproximately the midpoint of the alternating signal 17, V_(sig)(t)minimum, or zero, period. For example, the first primary ADC 50 a mayobtain a sample at times t₁, t₂=t₁+1/f_(d), t₃=t₁+2/f_(d) and so forth.

Referring in particular to FIG. 6B, as explained hereinbefore, theamplified signal 14 a may be approximated as a superposition of theintegrated output voltage signal V_(piezo)(t) and the capacitancemeasurement voltage signal V_(cap)(t). The capacitance measurementvoltage signal V_(cap)(t) is related to and has a similar form to thealternating signal 17, V_(sig)(t), and in particular has substantiallythe same frequency contents. When the capacitance measurement voltagesignal V_(cap)(t) is approximately in phase with the alternating signal17, V_(sig)(t), the synchronisation signal 53 will trigger sampling ofthe amplified signal 14 a at times when the contribution of thecapacitance measurement voltage signal V_(cap)(t) to the amplifiedsignal 14 a is substantially equal to a ground, common mode or minimumvalue. In this way, a sampling of substantially only the integratedoutput voltage signal V_(piezo)(t) may be obtained.

Referring in particular to FIG. 6C, the first filtered signal 15 a thentakes the form of a sequence of samplings of the integrated outputvoltage signal V_(piezo)(t) at times t₁, t₂, t₃ and so forth.

With the example of a pulsed wave as shown in FIG. 6A, small phaseshifts φ of up to about φ±π/2 between the capacitance measurementvoltage signal V_(cap)(t) and the alternating signal 17, V_(sig)(t), nooffset is required between the synchronisation signal 53 and thealternating signal 17, V_(sig)(t) in order to ensure that sampling ofthe first filtered signal 15 a occurs during low or zero signal level ofthe capacitance measurement voltage signal V_(cap)(t).

For larger phase shifts φ or different waveforms of the alternatingsignal 17, V_(sig)(t), an offset between the synchronisation signal 53and the alternating signal 17, V_(sig)(t) may be calibrated so that,within the range of capacitances expected/measured for the correspondingtouch panel 43, the synchronisation signal 53 triggers the first primaryADC 50 a during a period of low or zero signal level of the capacitancemeasurement voltage signal V_(cap)(t).

The first secondary ADC 51 a receives the amplified signal 14corresponding to a presently addressed third electrode 27 from the firstmultiplexer 49 a output. The first secondary ADC 51 a samples theamplified signal 14 a at a sampling frequency f_(cap), which is at leastseveral times the base frequency f_(d) of the alternating signal 17,V_(sig)(t). The first secondary ADC 51 a outputs a digitised amplifiedsignal 54 a to the controller 47. The controller 47 receives thedigitised amplified signal 54 a and applies a digital high pass filterto obtain the second filtered signal 16 in the digital domain. It willbe apparent that the synchronisation signal 53 has the effect oftriggering sampling of the amplified signal 14 a at times when theamplitude of the digitised amplified signal 54 a is substantially equalto a ground, common mode or minimum value. In this sense, the samplingof the first primary ADC 50 a is synchronised with the digitisedamplified signal 54 a.

Alternatively, since the integrated output voltage signal V_(piezo)(t)typically varies at frequencies several orders of magnitude less thanthe base frequency f_(d) of the alternating signal 17, V_(sig)(t), thecontroller 47 may treat the most recently sampled value of the firstfiltered signal 15, for example V_(piezo)(t₃), as an additional offsetand subtract this value from the digitised amplified signal 54 a. Moreaccurate baseline corrections may be employed, for example, linearinterpolation based on the two most recent sampled values of the firstfiltered signal 15, or quadratic interpolation based on the three mostrecently sampled values of the first filtered signal 15.

The primary and secondary ACDs 50, 51 may be the same. However, it maybe advantageous for the primary and secondary ADCs 50, 51 to bedifferent. In particular, the primary ADCs 50 a, 50 b may be optimisedfor the dynamic range of the integrated output voltage signalV_(piezo)(t), without the need to measure the larger amplitudescorresponding to the capacitance measurement voltage signal V_(cap)(t).Furthermore, because the first sampling frequency f_(piezo) should be atmost equal to the base frequency f_(d) of the alternating signal 17,V_(sig)(t), a lower bandwidth is required for the primary ADCs 50 a, 50b compared to the secondary ADCs 51 a, 51 b. For cost sensitiveapplications, this enables use of cheaper, ADCs for the primary ADCs 50a, 50 b. By contrast, for performance applications, this enables the useof more precise ADCs capable of differentiating a larger number ofsignal levels within the same dynamic range (a 16-bit ADC is typicallyslower than an 8-bit ADC all else being equal).

Similarly, each charge amplifier 52 of the second amplifier module 48 bis connected to a corresponding first electrode 7 via a respectiveterminal D1, . . . , D5 and conductive trace 45, and the output of eachcharge amplifier 50 of the second amplifier module 48 b is connected toa corresponding input of the second multiplexer 49 b. In this way, thesecond multiplexer 49 b may output an amplified signal 14 bcorresponding to an addressed first electrode 7 for filtering andprocessing by the second primary ADC 50 b, second secondary ADC 51 b andthe controller 47 in the same way as for signals corresponding to thethird electrodes 27. It will be apparent that the synchronisation signal53 has the effect of triggering sampling of the amplified signal 14 b attimes when the amplitude of the digitised amplified signal 54 b issubstantially equal to a ground, common mode or minimum value. In thissense, the sampling of the second primary ADC 50 b is synchronised withthe digitised amplified signal 54 a.

The controller 47 may also provide a second synchronisation signal 55 tothe multiplexers 49 a, 49 b and/or amplifiers 52. The secondsynchronisation signal 55 may cause the multiplexers 49 a, 49 b toaddress each combination of first and third electrodes 7, 27 accordingto a sequence determined by the controller 47. In this way, the firsttouch controller 44 may receive amplified signals 14 a, 14 b from eachpairing of first and third electrodes 7, 27 according to a sequencedetermined by the controller 47. The sequence may be pre-defined, forexample, the sequence may select each pair of a first electrode 7 and athird electrode 27 once before repeating. The sequence may bedynamically determined, for example, when one or more user interactionsare detected, the controller 47 may scan the subset of first electrodes7 and third electrodes 27 adjacent to each detected user interaction inorder to provide faster and/or more accurate tracking of user touches.The sequence may be arranged so that the multiplexors 49 a, 49 b addresseach pair of first and third electrodes 7, 27 during a quiet period orblanking period of the display 38. The sequence may be provided to thecontroller 47 by the processor 33 via the link 32. Alternatively, theprocessor 33 may directly control the sequence via the link 32.

Based on the obtained first filtered signals 15 a, 15 b the controller47 may calculate first pressure values 20 a corresponding to theaddressed third electrode 27 and second pressure values 20 bcorresponding to the addressed first electrode 7. The pressure values 20a, 20 b may be output via the link 32.

When the first touch controller 44 is operated in a self-capacitancemode, the controller 47 may provide suitable alternating signals 17,V_(sig)(t) to each amplifier 52 of the first and second amplifiermodules 48 a, 48 b. Based on the second filtered signals 16 obtained bythe controller 47 in the digital domain, the controller 47 may calculatefirst capacitance values 21 a corresponding to a self-capacitance of theaddressed third electrode 27 and second capacitance values 21 bcorresponding to a self-capacitance of the addressed first electrode 7.The capacitance values 21 a, 21 b may be output via the link 32.

When the first touch controller 44 is operated in a mutual-capacitancemode, the controller 47 may provide suitable alternating signals 17,V_(sig)(t) to each amplifier 52 of the first amplifier module 48 a.

In this way, an input of each amplifier 52 of the first amplificationmodule 48 a may be used to drive the corresponding third electrode 27 ofthe first touch panel 43 using the alternating signal 17, V_(sig)(t).Consequently, the input signals 10 received from a given third electrode27 and first electrodes 7 intersecting the given third electrode 27 maybe caused to vary in dependence upon a capacitive coupling between theelectrodes 7, 27, a user's digit or stylus and the capacitancemeasurement signal, and the input signals concurrently vary independence upon a strain of the layer of piezoelectric materialproximate to the given first electrode. In this way, the thirdelectrodes 27 may be transmitting, or Tx, electrodes and the firstelectrodes 7 may be receiving, or Rx, electrodes. Based on the secondfiltered signals 16 obtained by the controller 47 in the digital domain,the controller 47 calculates capacitance values 21 corresponding to amutual-capacitance between the addressed third electrode 27 and theaddressed first electrode 7. The capacitance values 21 are output viathe link 32.

Alternatively, alternating signals 17, V_(sig)(t) may be provided to thesecond amplifier module 48 b, the first electrodes 7 may betransmitting, or Tx, electrodes and the third electrodes 27 may bereceiving, or Rx, electrodes.

The processor 33 of the electronic device 29 receives the pressurevalues 20 a, 20 b and capacitance values 21 a, 21 b, 21 and may usethese to determine a location and an applied force corresponding to oneor more user interactions with the first touch panel 43. Alternatively,the locations and applied forces corresponding to user interactions maybe determined by the controller 47 and communicated to the processor 33via the link 32.

The controller 47 and/or the processor 33 may be calibrated to convertthe first filtered signals 15 a, 15 b into applied forces or pressuresby applying known pressures to known locations so that the accuracy ofcalculated positions and/or pressures of one or more user interactionsmay be optimised and/or verified.

Another difference between the first touch panel system 42 and the touchpanel systems described with reference to FIGS. 15 to 18, 21, and 25 to29 of WO 2016/102975 A2, is that in the first touch panel system 42 ofthe present specification, the amplified signals 14 a, 14 b aremultiplexed instead of the input signals 10. A consequence of providinga separate charge amplifier for each first and third electrode 7, 27 ofthe first touch panel 43 is that the size, complexity and cost of thefirst touch controller 44 is increased relative to the touch panelsystems described with reference to FIGS. 15 to 18, 21, and 25 to 29 ofWO 2016/102975 A2. It might be considered that it would make littledifference whether signals are multiplexed before or afteramplification, so that multiplexing before amplification would always bepreferred due to the reduction in size, complexity and cost possiblewhen fewer charge amplifiers are required.

However, in the specific application of combined pressure and capacitivesensing by separating a single amplified signal 14, it has beensurprisingly realised that multiplexing the amplified signals 14 insteadof the input signals 10 may provide improved performance. In particular,multiplexing the amplified signal 14 may improve the capture of chargesinduced in response to straining of the piezoelectric material layer 9at times when a particular electrode 7, 27 is not being addressed. Inother words, charges induced whilst other electrodes 7, 27 are beingread out. When the input signals to are multiplexed, any charge inducedon a non-addressed electrode will be stored on the input capacitance ofthe multiplexer. An input capacitance of a multiplexer is typicallysmall, and may show variations between different inputs which may besignificant in comparison to charges generated in response to strainingof the piezoelectric material layer 9. By contrast, when the amplifiedsignals 15 are multiplexed instead, charges induced when an electrode 7,27 is not being addressed may be stored in a capacitance of an amplifier52 feedback network (see FIG. 7), which may be both larger and moreconsistent. In this way, the first touch controller 44 may have improvedaccuracy in detecting the pressures of user interactions regardless ofthe timing of the user interaction with respect to a scanning/addressingsequence of the first and third electrodes 7, 27.

Additionally, multiplexing the amplified signals 14 instead of the inputsignals to may avoid problems with leakage current. In particular, theoff-state switches of a multiplexer will, in practice, leak smallcurrents over time. These small leakage currents corresponding to all ofthe inputs not being addressed by a multiplexor may add up and beintegrated by a charge amplifier, and the overall effect may becomparable to the charge or current corresponding to a user interactionproximate to an addressed electrode 7, 27. Such leakage currents maydegrade the sensitivity to applied pressures, and may also limitscalability, since a larger touch panel having a greater number ofelectrodes will need a correspondingly greater number of multiplexerchannels, increasing the leakage current. By contrast, when multiplexingthe amplified signals 14 the charge amplifiers 52 do not receive suchresidual currents.

In addition, it has been surprisingly realised that, in application tocombined pressure and capacitance sensing based on separating a singlesignal, multiplexing the amplified signals 15 may allow each chargeamplifier 52 to require a lower bandwidth and lower current capacity, ascompared to the requirements for charge amplifiers when the inputsignals 10 are multiplexed.

Retaining multiplexing before processing by the ADCs 50, 51 permits thefirst touch controller 44 to still be smaller and less complex thanproviding a wholly separate channel for each first and third electrode7, 27, since the ADCs 50, 51 do not need to be duplicated for eachelectrode 7, 27.

Modification Using a Single ADC:

Although the first touch panel system 42 has been described as includinga primary ADC 50 to obtain the first filtered signal 15 and a secondaryADC 51 to obtain the digitised amplified signal 54, a modified firsttouch panel system (not shown) may be implemented using a single ADC(not shown) which is capable of alternating operation at the first andsecond sampling frequencies f_(piezo), f_(cap). For example, a singleADC (not shown) may be controlled by the synchronisation signal 53 toobtain the first filtered signal 15 for a period, then subsequently beswitched to obtain the digitised amplified signal 54 for a period,before switching back to measure the first filtered signal 15 again. Thesingle ADC may be connectable to any one of the first or thirdelectrodes 7, 27 using a multiplexer or switching arrangement. In thisway, a single ADC can be used, in combination with digital filtering inthe controller 47, to obtain the first and second filtered signals 15,16 from a given first/third electrode 7, 27 sequentially. However, thesignals applied to the touch panel 43 and passing through the amplifiermodules 48 a, 48 b and multiplexers 49 a, 49 b remain the samethroughout, only the ADC sampling rate is varied. This may allow forsequential measurements of pressure and capacitance at a high rate andwith minimal impact from the switching.

By contrast, if the actual signals applied to the touch panel 43 were tobe switched, the switching rate would be limited by the inductance andcapacitance of the touch panel 43, traces 45, amplifiers 52 andmultiplexers 49 a, 49 b.

In this way, the implementation of sequential, alternating operation atthe first and second sampling frequencies f_(piezo), f_(cap) reduces thenumber of ADCs required. Even though the single ADC (not shown) must becapable of operation up to the second sampling frequency f_(cap), thepower draw when sampling at the first sampling frequency f_(piezo) maybe relatively reduced.

Example of Charge Amplifiers:

Referring also to FIG. 7, an example of one configuration of chargeamplifiers 52 a, 52 b suitable for use in the first and second amplifiermodules 48 a, 48 b is shown.

In one configuration, each charge amplifier 52 a, 52 b includes anoperational amplifier OP having an inverting input, a non-invertinginput and an output. For example, each charge amplifier 52 a formingpart of the first amplifier module 48 a includes an operationalamplifier OP having an inverting input coupled to a correspondingterminal C via an input resistance R_(i) and a first switch SW1connected in series. The non-inverting input of the operationalamplifier OP is connected to an alternating signal 17, V_(sig)(t). Thealternating signal 17, V_(sig)(t) may be provided by the controller 47,by a separate module of the first touch controller 44, or may bereceived into the first touch controller 44 from an external source.Since the inverting input will be at practically the same voltage as thenon-inverting input, the non-inverting input can be caused to drive thecorresponding third electrode 27. A feedback network of the chargeamplifier 52 a includes a feedback resistance R_(f), a feedbackcapacitance C_(f) and a second switch SW2 connected in parallel betweenthe inverting input and the output of the operational amplifier OP. Theoutput of the operational amplifier V_(out) provides the amplifiedsignal 14.

In the example shown in FIG. 7, the first touch controller 44 isconfigured for mutual capacitance measurements between each pair offirst and third electrodes 7, 27. Each charge amplifier 52 b formingpart of the second amplifier module 48 b is the same as each chargeamplifier 52 a of the first amplifier module 48 a, except that thenon-inverting input of the operational amplifier OP is coupled to acommon mode voltage V_(CM) instead of the alternating signal 17,V_(sig)(t), and in that the inverting input is connected to a terminal Dinstead of a terminal C.

Other terminals of the operational amplifiers OP, such as power supplyterminals, may be present, but are not shown in this or other schematiccircuit diagrams described herein.

The second switches SW2 permit the corresponding feedback capacitorsC_(f) to be discharged. The opening and closing of the second switchesSW2 may be governed by the second synchronisation signal 55 provided bythe controller 47. In this way, the feedback capacitors C_(f) of eachcharge amplifier 52 a, 52 b may be periodically discharged in order toreset the feedback network of the operational amplifier OP to preventexcessive drift. Similarly, the first switches SW1 may be controlled bythe second synchronisation signal 55 provided by the controller 47 toenable an amplifier 52 a, 52 b to be connected or disconnected from thecorresponding electrode 7, 27 if required.

Second Touch Panel System:

Referring also to FIG. 8, a second touch panel system 56 includes thefirst touch panel 43 and a second touch controller 57 for combinedpressure and capacitance sensing.

The second touch controller 57 is the same as the first touch controller44, except that in the second touch controller 57 the input signals tofrom a third electrode 27 are connected to a single charge amplifier 52a by a first multiplexer 49 a. The charge amplifier 52 a outputs theamplified signal 14 a, which is processed by the primary ADC boa, thesecondary ADC 51 a and the controller 47 to obtain the first and secondfiltered signals 15, 16 in the same way as for the first touchcontroller 44. Similarly, the input signals to from a first electrode 7are connected to a single charge amplifier 52 b by a second multiplexer49 b. The charge amplifier 52 b outputs the amplified signal 14 b, whichis processed by the primary ADC 50 b, the secondary ADC 51 b and thecontroller 47 to obtain the first and second filtered signals 15, 16 inthe same way as for the first touch controller 44.

In the same way as the first touch controller 44, use of primary andsecondary ADCs 50, 51 is not essential. Instead, a single ADC (notshown) which is capable of alternating operation at the first and secondsampling frequencies f_(piezo), f_(cap) so as to obtain the first andsecond filtered signals 15, 16 sequentially.

Example of Charge Amplifiers:

Referring also to FIG. 9, an example of one configuration of chargeamplifiers 52 a, 52 b for the second touch controller 57 is shown.

The charge amplifiers 52 a, 52 b of the second touch controller 57 maybe configured in the same way as the charge amplifiers 52 a, 52 b of theamplifier modules 48 a, 48 b of the first touch controller 44, exceptthat the inverting input of the operational amplifiers OP are coupled tothe corresponding outputs of the multiplexers 49 a, 49 b via respectiveinput resistances R_(i). Each input of the first multiplexer 49 a iscoupled to one of a number, N, of input terminals C1, C2, . . . , CN.Each input of the second multiplexer 49 b is coupled to one of a number,M, of input terminals D1, D2, . . . , DM.

Third Touch Panel System:

Referring also to FIG. 10, a third touch panel system 58 includes asecond touch panel 59 and the first touch controller 44 for combinedpressure and capacitance sensing.

The second touch panel 59 includes a layer structure 4 which isgenerally the same as the first layer structures 4 of the first touchsensor 2, except that multiple first electrodes 7 are disposed on thefirst face 5 of the first layer structure 4 and that multiple secondelectrodes 8 are disposed on the second face 6 of the first layerstructure 4.

The first electrodes 7 each extend in the first direction x and thefirst electrodes 7 are disposed in an array evenly spaced in the seconddirection y. The second electrodes 8 each extend in the second directiony and the second electrodes 8 are disposed in an array evenly spaced inthe first direction x. Each first electrode 7 and each second electrode8 is coupled to a corresponding conductive trace 45.

In this way, the area around each intersection of a first electrode 7with a second electrode 8 effectively provides a first touch sensor 2.

The second touch panel 59 may be bonded overlying the display 38 of anelectronic device 29. In this case, the materials of the second touchpanel 59 should be substantially transparent as described hereinbefore.A cover lens 46 (FIG. 20) may be bonded overlying the second touch panel59. The cover lens 46 (FIG. 20) is preferably glass but may be anytransparent material. The cover lens 46 (FIG. 20) may be bonded to thesecond touch panel 59 using a layer of pressure sensitive adhesive (PSA)material (not shown). The layer of PSA material (not shown) may besubstantially transparent. The first and second electrodes 7, 8 may befabricated using index matching techniques to minimise visibility to auser.

Each first electrode 7 is connected to the input of a correspondingcharge amplifier 52 a of the first amplification module 48 a of thefirst touch controller 44 via a respective terminal A1, A2, . . . , A5.Similarly, each second electrode 8 is connected to the input of acorresponding charge amplifier 52 b of the second amplification module48 b of the first touch controller 44 via a respective terminal B1, B2,. . . , B5.

Fourth Touch Panel System:

A fourth touch panel system (not shown) includes the second touch panel59 connected to the second touch controller 57 for combined pressure andcapacitance sensing.

Alternative Electrode Geometries:

In the first touch panel 43, the first and third electrodes 7, 27 havebeen shown in the form of elongated rectangular electrodes. However,other shapes may be used.

Referring also to FIG. 11, an alternative geometry of the first andthird electrodes 7, 27 is shown.

Instead of being rectangular, each first electrode 7 may include severalpad segments 60 evenly spaced in the first direction x and connected toone another in the first direction x by relatively narrow bridgingsegments 61. Similarly each third electrode 27 may comprise several padsegments 62 evenly spaced in the second direction y and connected to oneanother in the second direction y by relatively narrow bridging segments63. The pad segments 60 of the first electrodes 7 are diamonds having afirst width W1 in the second direction y and the bridging segments 61 ofthe first electrodes 7 have a second width W2 in the second direction y.The pad segments 62 and bridging segments 63 of the third electrodes 27have the same respective shapes and widths W1, W2 as the firstelectrodes 7.

The first electrodes 7 and the third electrodes 27 are arranged suchthat the bridging segments 63 of the third electrodes 27 overlie thebridging segments 61 of the first electrodes 7. Alternatively, the firstelectrodes 7 and the third electrodes 27 may be arranged such that thepad segments 62 of the third electrodes 27 overlie the pad segments 60of the first electrodes 7. The pad segments 60, 62 need not be diamondshaped, and may instead be circular. The pad segments 60, 62 may be aregular polygon such as a triangle, square, pentagon or hexagon. The padsegments 60, 62 may be I shaped or Z shaped.

The alternative geometries of first and third electrodes 7, 27 of thefirst touch panel 43 are equally applicable to the first and secondelectrodes 7, 8 of the second touch panel 59.

Third Touch Panel:

Referring also FIG. 12, a third touch panel 64 may be included in thefirst or second touch panel system 42, 56 instead of the first touchpanel 43.

The third touch panel 64 is substantially the same as the first touchpanel 43 except that the third touch panel 64 does not include thesecond layer structure 24 and the third electrodes 27 are disposed onthe first face 5 of the first layer structure 4 in addition to the firstelectrodes 7. Each first electrode 7 is a continuous conductive regionextending in the first direction x. For example, each first electrode 7may include several pad segments 65 evenly spaced in the first directionx and connected to one another in the first direction x by relativelynarrow bridging segments 66. Each third electrode 27 may compriseseveral pad segments 67 evenly spaced in the second direction y.However, the pad segments 67 of the third electrodes 27 are disposed onthe first face 5 of the first layer structure 4 and are interspersedwith, and separated by, the first electrodes 7. The pad segments 67corresponding to each third electrode 27 are connected together byconductive jumpers 68. The jumpers 68 each span a part of a firstelectrode 7 and the jumpers 68 are insulated from the first electrodes 7by a thin layer of dielectric material (not shown) which may belocalised to the area around the intersection of the jumper 68 and thefirst electrode 7.

Alternatively, a dielectric layer (not shown) may overlie the first face5 of the first layer structure 4 and the first and third electrodes 7,27. Conductive traces (not shown) extending in the second direction ymay be disposed over the dielectric layer (not shown), each conductivetrace (not shown) overlying the pad segments 67 making up one thirdelectrode 27. The overlying conductive traces (not shown) may connectthe pad segments 67 making up each third electrode 27 using vias (notshown) formed through the dielectric layer (not shown).

Patterned Second Electrode:

Referring also to FIG. 13, a patterned second electrode 69 is in theform of a Cartesian grid. The conductive region of the patterned secondelectrode 69 includes struts 70 extending in the first direction x andhaving a width W in the second direction y, and struts 71 extending inthe second direction y and having a width W in the first direction x.The struts 700 extending in the first direction x are evenly spaced inthe second direction y with a spacing S, and the struts 71 extending inthe second direction y are evenly spaced in the first direction x withthe same spacing S. The struts 70, 71 are joined where they intersectsuch that the patterned second electrode 69 is formed of a single regionof conductive material.

The patterned second electrode 69 may be arranged such that themagnitude of a mutual capacitance between the first electrode 7 and thesecond electrode 8 is reduced in the first touch panel 43. This mayincrease the relative size of changes in the mutual capacitance betweenthe first electrode 7 and the second electrode 8 resulting from a userstouch, making such changes easier to detect.

Additionally or alternatively, the patterned second electrode 69 may beplaced between the first and/or third electrodes 7, 27 and a user'sdigit or stylus without entirely screening the first and/or thirdelectrodes 7, 27 from electrostatic interactions with the user's digitor stylus.

Fourth Touch Panel:

Referring also to FIGS. 14 and 15, a fourth touch panel 72 is shown.

The fourth touch panel 72 includes the first layer 4, a plurality offirst electrodes 7 disposed on the first face 5 of the first layerstructure 4, a plurality of third electrodes 27 disposed on the secondface 6 of the first layer structure 4 and a plurality of secondelectrodes 8 disposed on the second face 6 of the layer structure 4 inthe form of a plurality of separated second electrodes 73.

The first electrodes 7 extend in the first direction x and are spacedapart in the second direction y. The third electrodes 27 extend in thesecond direction y and are spaced apart in the first direction x. Theseparated second electrodes 73 extend in the second direction y arespaced apart in the first direction x. The separated second electrodes73 and the third electrodes 27 are interleaved and do not contact oneanother. The separated second electrodes 73 and the third electrodes 27could also be described as interdigitated. The separated secondelectrodes 73 and third electrodes 27 may be read using conductivetraces (not shown) which exit the fourth touch panel 72 on differentedges. Each first electrode 7 may take the form of several pad segments74 evenly spaced in the first direction x and connected to one anotherin the first direction x by relatively narrow bridging segments 75.Similarly, each third electrode 27 may include several pad segments 76evenly spaced in the second direction y and connected to one another inthe second direction y by relatively narrow bridging segments 77. Thepad segments 74 of the first electrodes 7 may be diamond shaped. The padsegments 76 and bridging segments 77 of the third electrodes 27 may havethe same respective shapes and widths as the first electrodes 7. Eachseparated second electrode 73 may include several pad segments 78 evenlyspaced in the second direction y and connected to one another in thesecond direction y by relatively narrow bridging segments 79. The padsegments 78 and bridging segments 79 of the separated second electrodes73 may have the same respective shapes and widths as the first and thirdelectrodes 7, 27. Alternatively, the pad segments 74 of the firstelectrodes 7 may be larger or smaller than the pad segments 78 of theseparated second electrodes 72.

The first electrodes 7 and the third electrodes 27 are arranged suchthat the bridging segments 77 of the third electrodes 27 overlie thebridging segments 75 of the first electrodes 7. The first electrodes 7and the third electrodes 27 are arranged such that the respective padsegments 74, 76 do not overlap. Instead, the separated second electrodes73 are arranged such that the pad segments 78 of the separated secondelectrodes 73 overlap the pad segments 74 of the first electrodes 7. Thepad segments 74, 76, 78 need not be diamond shaped, and may instead becircular. The pad segments 74, 76, 78 may be a regular polygonal shapesuch as a triangle, square, pentagon or hexagon.

The fourth touch panel 72 may be used in, for example, the first orsecond touch panel systems 42, 56 to measure mutual capacitance betweena pair of first and third electrodes 7, 27. The separated secondelectrodes 73 may be coupled to each another, for example using externaltraces (not shown) and addressed collectively to measure pressure valuesbetween a first electrode 7 and the separated second electrodes 73and/or between a third electrode 27 and the separated second electrodes73. Alternatively, the separated second electrodes 72 may beindividually addressable to measure pressure values using a pair offirst and separated second electrodes 7, 73 and/or a pair of third andseparated second electrode 27, 73.

Pre-Amplification Signal Separation:

In the first and second touch panel systems 42, 56, a single inputsignal 10 including both pressure and capacitance information isreceived from an electrode 7, 8, 27, before being amplified to generatean amplified signal 14 which is subsequently processed to obtain a firstfiltered signal 15 containing pressure information and a second filteredsignal 16 containing capacitance information.

In an alternative approach to combined pressure and capacitance sensing,a single input signal to including pressure and capacitance informationmay be separated into pressure and capacitance processing channelsbefore amplification. Touch panel systems employing post separationamplification can also benefit from many of the improvements provided bymultiplexing amplified signals from a plurality of amplifiers.

Referring also to FIG. 16, a third apparatus 80 for combined pressureand capacitance sensing is shown.

The third apparatus 80 includes a first touch sensor 2 and analternative front end module 81. The alternative front end module 81includes a signal separation stage 82 and an amplification stage 83. Thealternative front end module 81 is connected to the touch sensor 2, acapacitive touch controller 84 and a pressure signal processing module85. The alternative front end module 81 allows capacitance and pressuremeasurements to be made from the first touch sensor 2 concurrently usingone pair of electrodes 7, 8.

The alternative front end module 81 includes a first input/outputterminal A for connecting to the touch sensor 2 and a secondinput/output terminal F for connecting to the capacitive touchcontroller 84. The signal separation stage 82 includes a high-passfilter 86. The signal separation stage 82 connects the firstinput/output terminal A to the second input/output terminal F via thehigh-pass filter 86. The high-pass filter 86 filters signals between thesecond input/output terminal F and the first input/output terminal A.The signal separation stage 82 also connects the amplification stage 83to the first input/output terminal A. Signals between the firstinput/output terminal A and the amplification stage 83 are not filteredby the high-pass filter 86.

The amplification stage 83 is connected to the first input/outputterminal A through the signal separation stage 82. The amplificationstage 83 includes an amplifier having characteristics of a low-passfilter, for example, an operational amplifier and aresistance-capacitance feedback network. The amplification stage 83receives an input signal 87 from an electrode 7 of the touch sensor 2,and high-frequency components above a band-stop frequency of theamplification stage are rejected, or at least attenuated, whereasfrequency components below the band-stop frequency, including theintegrated output voltage signal V_(piezo)(t), are amplified to producean amplified signal 88. The rejection of high frequency components bythe amplification stage 83 input is, in practice, imperfect, with theresult that the amplified signal 88 may still include significantunwanted contributions from the capacitance measurements. Consequently,further filtering of the amplified signal 88 in the digital domain couldbe employed to reduce interference from capacitance measurements.However, this may increase computational requirements for the pressuresignal processing module 85.

In the same way as for the first to fourth touch panel systems 42, 56,58, the amplified signal 88 may be sampled whilst reducing or avoidinginterference from capacitance measurements by sampling the amplifiedsignal 88 at the first sampling frequency f_(piezo) using an ADC 89which is synchronised with the capacitance measurements using asynchronisation/dock signal 900 supplied by the capacitive touchcontroller 84. For example, the synchronisation signal go may be adocking signal of the capacitive touch controller 84 or may be theactual driving signal for capacitance measurements. The ADC 89 outputsthe filtered amplified signal 94 to the pressure signal processingmodule 85.

Alternatively, the pressure signal processing module 85, or even aseparate synchronisation module (not shown) may receive a clockingsignal of the capacitive touch controller 84, or the actual drivingsignal for capacitance measurements and, based on these inputs, generatethe synchronisation signal 900 for the ADC 89.

The amplification stage 83 may have a low-frequency cut-off configuredto reject a pyroelectric response of the layer of piezoelectric material9. The low frequency cut-off may take a value between 1 Hz and 7 Hz. Theamplification stage 83 may include a notch filter configured to reject amains power distribution frequency, for example, 50 Hz or 60 Hz.Alternatively, the mains power notch filter may be a separate filterstage (not shown) disposed before or after the amplification stage 83.

The capacitive touch controller 84 is, in general, a conventionalcapacitive touch controller capable of measuring the self-capacitance ormutual capacitance of a projected capacitance touch panel electrode. Forexample, the capacitive touch controller may be a commercially availabletouch controller such as an Atmel® MXT224 touch controller. For example,for a mutual capacitance measurement, the capacitive touch controller 84outputs a capacitance measurement drive signal 91 which drives thesecond electrode 8 as a transmitting or Tx electrode. The firstelectrode 7 serves as a receiving or Rx electrode and picks up areceived signal 92 based on the drive signal 91 and a mutual capacitancebetween the first and second electrodes 7, 8. The drive and receivedsignals 91, 92 typically have the same frequency contents. The high-passfilter 86 has a frequency response which passes the drive/receivedsignals 91, 92, which are typically at least to kHz, without attenuationor with minimal attenuation. Based on the transmitted drive signal 91and the received signal 92, the capacitive touch controller 84calculates a mutual capacitance value and provides an output comprisingcapacitance values 93.

The specific method and the specific waveforms of the capacitancemeasurement drive signals 91 depend on the particular capacitive touchcontroller 84 used. However, any capacitive touch controller 84 may beused with the alternative front end module 81 by adjusting the lowerband-stop frequency of the high-pass filter 86 to pass the capacitancemeasurement drive signals 91 produced by a particular capacitive touchcontroller 84 and picked up as received signal 92.

The input signal 87 may differ slightly from the received signal inresponse to a user interaction with the first touch sensor 2, or with alayer of material overlying the first touch sensor 2, which in eithercase might produce a piezoelectric response from the layer ofpiezoelectric material 9. In this way, the input signal 87 isapproximately a superposition of a received signal 92 and apiezoelectric response I_(piezo)(t). Because the high-pass filter 86 isadapted to pass the received signal 92, the capacitive touch controller84 may communicate with the touch sensor 2 and receive the receivedsignal 92 with no, or minimal, interference from the piezoelectricresponse I_(piezo)(t). In this way, a capacitive touch controller 84suitable for use with a conventional projected capacitance touch panelcan be used with the alternative front end module 81.

The amplification stage 83 is adapted to reject, or at least attenuate,the received signals 92. In this way, the amplified signal 88 may besubstantially based on an integrated output voltage signal V_(piezo)(t)corresponding to the piezoelectric response I_(piezo)(t) produced bystraining the layer of piezoelectric material 9. As explainedhereinbefore, the synchronisation of the ADC 89 may further reduce anyresidual components of the received signals 92 in the filtered amplifiedsignal 94. In this way, the amplitude of the filtered amplified signal94 is dependent upon a pressure applied to the first touch sensor 2.

The separation of the received signals 92 and the piezoelectric responseI_(piezo)(t) is possible because, as described hereinbefore, thesesignals have dissimilar and generally separable frequency bandwidths.

The pressure signal processing module 85 receives the filtered amplifiedsignals 94, determines pressure values 95, and provides the pressurevalues 95 as an output. The pressure signal processing module 85 maydetermine the pressure value 95 corresponding to a given filteredamplified signal 94 using, for example, a pre-calibrated empiricalrelationship, or by interpolation of a pre-calibrated look-up table.

In this way, the third apparatus 800 may be used for combined pressureand capacitance sensing, although in a different way to the first orsecond apparatus 1, 22 or first or second touch panel systems 42, 56.Compared to the first or second apparatus 1, 22 or first or second touchpanel systems 42, 56, the third apparatus 800 allows the separation andamplification of pressure and capacitance signals in a way which may bereadily integrated with existing projected capacitance touch panels andcapacitive touch controllers 84.

Alternatively, the third apparatus 800 may be used with a capacitivetouch controller 84 which measures self-capacitance, in which case theself-capacitance measurement signal (not shown) would be provided to thefirst electrode 7 via the signal separation stage 82 and high-passfilter 86. In this case, the capacitive touch controller 84 may alsooutput a biasing signal to the second electrode 8 to screen out themutual capacitance between the first and second electrodes 7, 8.

The third apparatus 80 may also be used with the second touch sensor 23,for example a third apparatus 80 may be connected to each of the firstand third electrodes 7, 27.

Fifth Touch Panel System:

Touch panel systems including touch panels including multiple touchsensors 2, 23 combined with apparatus for combined capacitance andpressure sensing employing pre-amplification signal separation have beendescribed in GB 2544353 A, in particular with reference to FIGS. 5, 10to 12, 15 and 19 to 23 of this document. Touch panel systems describedin GB 2544353 A implement isolation of the piezoelectric response usinghardware filters or software filtering in the digital domain. Thus, byusing the approach of the present specification and employing an ADC 89synchronised to low or zero signal level of capacitance measurementsignals, touch panel systems of the present invention may obtain theadvantages described hereinbefore in relation to the first touch panelsystem 42.

Further, in the touch panel systems described in GB 2544353 A, anamplifier was provided corresponding to each electrode, or severalelectrodes were connected to a smaller number of amplifiers by animpedance network to produce aggregated pressure signals.

The multiplexing of amplified signals described in relation to the firstand second touch panel systems 42, 56 may also be employed in thecontext of pre-amplification signal separation and may obtain many ofthe same effects. In particular, multiplexing of amplified signalsallows a reduction in the number of ADCs required.

Referring also to FIG. 17, a fifth touch panel system 96 includes thefirst touch panel 43 and a third touch controller 97 for combinedpressure and capacitance sensing.

The first touch panel 43 may be bonded overlying the display 38 of anelectronic device 29. In this case, the materials of the first touchpanel 43 should be substantially transparent as described hereinbefore.A cover lens 46 (FIG. 21) may be bonded overlying the first touch panel43. The cover lens 46 (FIG. 21) is preferably glass but may be anytransparent material. The cover lens 46 (FIG. 21) may be bonded to thefirst touch panel 43 using a layer of pressure sensitive adhesive (PSA)material 109 (FIG. 22). The layer of PSA material 109 (FIG. 22) may besubstantially transparent. The first and third electrodes 7, 27 may befabricated using index matching techniques to minimise visibility to auser.

The third touch controller 97 includes a capacitive touch controller 84,a number of signal separation stages 82, an amplification stage 83, amultiplexer 98, an ADC 89 and a controller 99. The controller 99 maycommunicate with the processor 33 of the electronic device 29 using alink 32.

Each separation stage 82 includes a high-pass filter 86. Theamplification stage 83 includes a number of charge amplifiers 100. Eachamplifier 100 is configured to reject, or at least attenuate, thereceived signals 92. Each charge amplifier 100 of the amplificationstage 83 is connected to a corresponding first electrode 7 via arespective terminal D1, . . . , D5 and conductive trace 45. The outputsof the charge amplifiers 100 of the amplification stage 83 are eachconnected to a corresponding input of the multiplexer 98. In this way,the multiplexer 98 may output an amplified signal 88 corresponding to anaddressed first electrode 7. The amplified signal 88 is converted into afiltered amplified signal 94 by the ADC 89 by sampling during low orzero periods of the capacitance drive signal 91. In the third touchcontroller 97, the capacitive touch controller 84 provides the drivesignal 91 to the controller 99, and based on the drive signal 91 thecontroller 99 provides the synchronisation signal 90 to the ADC 89. Inthe third touch controller 97, the controller 99 provides the functionsof the pressure signal processing module 85. The ADC 89 may beintegrated with the controller 99. The controller 99 determines pressurevalues 95 and outputs the pressure values 95 via the link 32.

The capacitive touch controller 84 is connected to each third electrode27 via a respective terminal C1, . . . , C5 to supply capacitancemeasurement driving signals 91 to the third electrodes 27. In theexample shown in FIG. 17, the third electrodes 27 serve as transmitting,Tx, electrodes and the first electrodes 7 serve as receiving, Rx,electrodes for mutual capacitance measurements. If the capacitive touchcontroller 84 has fewer driving outputs than there are third electrodes27, a further multiplexer (not shown) may be included to enable drivingof each third electrode 27. The capacitive touch controller 84 mayoutput capacitance values 93 to the controller 99 for output via thelink 32, or may have direct access to the link 32 for outputtingcapacitance values 93.

The controller 99 may provide a second synchronisation signal 100 to themultiplexer 98 and/or amplifiers 100. The second synchronisation signallot may cause the multiplexer 98 to address each first electrode 7according to a sequence determined by the controller 99. The controller99 may also provide the second synchronisation signal 101 to thecapacitive touch controller 84 to cause the capacitive touch controller84 to drive each third electrode 27 according to a sequence determinedby the controller 99. In this way, the third touch controller 97 mayobtain pressure and capacitance information corresponding to eachpairing of a first electrode 7 and a third electrode 27 according to asequence which may be predetermined or dynamically determined in thesame way as for the first and second touch controllers 44, 56.

In the example shown in FIG. 17, the fifth touch panel system 96 allowsmeasurements of two-dimensional mutual capacitance information in thefirst and second directions x, y, and one-dimensional pressureinformation in the first direction x. In alternative examples, a secondpressure measurement channel including signal separation stages 82, anamplification module 83 and a multiplexer 98 may be provided for thethird electrodes 27 to add another dimension of pressure sensing. Inthis latter case, the capacitive touch controller 84 may drive the thirdelectrodes 27 through the signal separation stages 82 of the secondpressure measurement channel.

In the example shown in FIG. 17, the capacitive touch controller 84performs mutual capacitance measurements. Alternatively, the capacitivetouch controller 84 may perform self-capacitance measurements of thefirst and third electrodes 7, 27 individually.

The capacitive touch controller 84 does not need to be a separate modulewithin the third touch controller 97, and alternatively may beintegrated with the controller 99. In other examples, the capacitivetouch controller 84 may be provided separately from the third touchcontroller 97, which may facilitate augmenting an existing projectedcapacitance touch system with pressure sensing on one or both of x- andy-electrodes.

Using the ADC 89 synchronised to sample during low or zero signalperiods of the capacitance measurement signal may provide some or all ofthe same effects as in the first and second touch systems 42, 56.Similarly, multiplexing of the amplified signals 88 may provide some orall of the same effects as in the first and second touch systems 42, 56.

The third touch controller 97 may alternatively be used with the second,third or fourth touch panels 59, 64, 72 instead of the first touch panel43.

Example of Charge Amplifiers:

Referring also to FIG. 18, an example of one configuration of the chargeamplifiers 100 and signal separation stages 82 is shown for the thirdtouch controller 97.

In one configuration, each charge amplifier 100 includes an operationalamplifier OP having an inverting input, a non-inverting input and anoutput. Each charge amplifier 100 forming part of the amplificationmodule 83 includes an operational amplifier OP having an inverting inputcoupled to a corresponding terminal D via an input resistance R₂ and afirst switch SW1 connected in series. The non-inverting input of theoperational amplifier OP is connected to a common mode voltage V_(CM). Afeedback network of the charge amplifier 100 includes a feedbackresistance R_(f), a feedback capacitance C_(f) and a second switch SW2connected in parallel between the inverting input and the output of theoperational amplifier OP. The output of the operational amplifierV_(out) provides the amplified signal 88.

The capacitive touch controller 84 is connected to a node 102 betweenthe input resistance R₂ and the terminal D via a resistance R₁ andcapacitance C₁ connected in series. The resistances R₁, R₂, capacitanceC₁ and node 102 together form the signal separation stage 82 in theexample shown in FIG. 17. The high-pass filter 86 takes the form of thecapacitance C₁. The feedback resistance and capacitance R_(f), C_(f), incombination with the input resistance R₂, control the frequencydependence of the amplifier 100, and are selected to attenuate thedrive/received signals 91, 92.

Other terminals of the operational amplifier OP, such as power supplyterminals, may be present, but are not shown in this or other schematiccircuit diagrams described herein.

The second switches SW2 permit the corresponding feedback capacitorsC_(f) to be discharged. The opening and closing of the second switchesSW2 may be governed by the second synchronisation signal 101 provided bythe controller 99. In this way, the feedback capacitors C of each chargeamplifier 100 may be periodically discharged in order to reset thefeedback network of the operational amplifier OP to prevent excessivedrift. Similarly, the first switches SW1 may be controlled by the secondsynchronisation signal tot provided by the controller 99 to enableconnection or disconnection from the corresponding first electrode 7 asrequired.

Sixth Touch Panel System:

Referring also to FIG. 19, a sixth touch panel system 103 includes thefirst touch panel 43 and a fourth touch controller 104 for combinedpressure and capacitance sensing.

The fourth touch controller 104 is the same as the third touchcontroller 97, except that the order of amplification and multiplexingis reversed. In the fourth touch controller 104, each input of themultiplexer 98 received input signals 87 via a respective signalseparation stage 82, and the multiplexer 98 output is provided to anamplification module 83 in the form of a single charge amplifier 100.The processing of the amplified signals 88 is the same as for the thirdtouch controller 97.

Referring also to FIG. 20, an example of one configuration of the chargeamplifiers 100 and signal separation stages 82 is shown for the fourthtouch controller 1004.

The charge amplifier 100 is configured the same as for each of thecharge amplifiers 100 of the third touch controller 97 (FIG. 18), exceptthat the inverting input of the operational amplifier OP is connected toa signal separation stages 82 via the multiplexer 98.

Touch Display Stack-Ups:

The first, second, third and fourth touch controllers 44, 57, 97, 104may be used in combination with a variety of different touch displaystack-ups. The following examples are intended for illustrative purposesand are not exhaustive.

Referring also to FIG. 21, a first display stack-up 105 is shown.

The first display stack-up 105 includes a display 38, the secondelectrode 8, the layer of piezoelectric material 9, a first dielectriclayer 106, the first electrodes 7, a second dielectric layer 107, thethird electrodes 27 and a cover lens 46, stacked in the thicknessdirection z from the display 38 to the cover lens 46. The first layerstructure 4 includes the layer of piezoelectric material 9 and the firstdielectric layer 1006. The second layer structure 24 corresponds to thesecond dielectric layer 107.

The first electrodes 7 take the form of a set of conductive regionsextending in the second direction y and spaced apart in the firstdirection x, and are disposed on the first dielectric layer 106. Thethird electrodes 27 take the form of a set of conductive regionsextending in the first direction x and spaced apart in the seconddirection y, and are disposed on the second dielectric layer 107. Thesecond electrode 8 takes the form of a conductive material regiondisposed on the layer of piezoelectric material 9 such that the secondelectrode 8 at least partially overlaps each first electrode 7 and eachthird electrode 27.

The cover lens 46 is made of glass, or PET or any other substantiallytransparent material. The cover lens 46 may be up to about 20 mm thickand may be at least 0.05 mm thick. Preferably, the cover lens 46 is upto about 2 mm thick and may be at least 0.05 mm thick. The layer ofpiezoelectric material 9 is made of PVDF or any other substantiallytransparent piezoelectric material. An alternative material ispolylactic acid. The layer of piezoelectric material may be up to about110 μm thick, and may be at least 0.5 μm or at least 1 μm thick. Thedielectric layers 106, 107 may be PET or any other substantiallytransparent polymer. The dielectric layers 106, 107 may be between 10 μmand 100 μm thick, for example, around 20 to 25 μm thick. Preferably thedielectric layers 106, 107 are in the range of about 10-100 μm thick.The conductive regions providing the electrodes 7, 8, 27 may be ITO, IZOor any other substantially transparent conductive material. Theconductive regions providing the electrodes 7, 8, 27 may be applied tothe dielectric layers 106, 107 and/or the layer of piezoelectricmaterial 9 using lithography, printing or other suitable methods. Theshapes of the conductive regions providing the first, second and thirdelectrodes 7, 8, 27 may be any suitable electrode shape described inrelation to the first or second touch panels 43, 59. The sheetresistance of conductive regions providing electrodes may be between 1and 200 Ω/sq. The sheet resistance may be below 10 Ω/sq. Preferably, thesheet resistance is as low as is practical.

Referring also to FIG. 22, a second display stack-up 108 is shown.

The second display stack-up 108 is the same as the first displaystack-up 1005, except that elements of the second display stack-up 108are bonded to one another using layers of pressure sensitive adhesive(PSA) material 109 extending in the first x and second y directions.

Referring also to FIG. 23, a first embedded stack-up 110 is shown. Thefirst embedded stack-up 110 includes a pixel array 111 of a display 38,a colour filter glass 112, first electrodes 7, a first layer structure4, third electrodes 27, a polariser 113 and a cover lens 46 stacked inthe thickness direction z from the pixel array 111 to the cover lens 46.The third electrodes 27 may be disposed on the first layer structure 4and the first electrodes 7 may be disposed on the colour filter glass112. Alternatively, the third electrodes 27 may be disposed on the firstface 5 of the first layer structure 4 and the first electrodes 7 may bedisposed on the second face 6 of the first layer structure 4. In someexamples, the first layer structure 4 may include only the layer ofpiezoelectric material 9, in which case the first and third electrodes7, 27 may be disposed on opposite faces of the layer of piezoelectricmaterial 9.

By omitting the second electrode 8, 69, the display stack-up may besimplified and may also be thinner as fewer layers are required.Additionally, even a patterned second electrode 69 will partially shieldthe first and third electrodes 7, 27, and thus reduce the sensitivity ofcapacitive touch measurements, if located between a user and the firstand third electrodes 7, 27. Such problems may be avoided using the firstembedded stack-up 110.

Referring also to FIG. 24, a second embedded stack-up 114 is shown. Thesecond embedded stack-up 114 is the same as the first embedded stack-up110, except that the order of the first electrodes 7 and the colourfilter glass 112 is reversed, so that the second embedded stack-up 114includes a pixel array 111 of a display 38, first electrodes 7, a colourfilter glass 112, a first layer structure 4, third electrodes 27, apolariser 113 and a cover lens 46 stacked in the thickness direction zfrom the pixel array 1 n to the cover lens 46.

MODIFICATIONS

It will be appreciated that many modifications may be made to theembodiments hereinbefore described. Such modifications may involveequivalent and other features which are already known in the design,manufacture and use of pressure-sensing projected capacitance touchpanels and which may be used instead of or in addition to featuresalready described herein. Features of one embodiment may be replaced orsupplemented by features of another embodiment.

Examples described hereinbefore have been illustrated in theaccompanying drawings including specific numbers of electrodes for thepurposed of illustration only. Examples according to the presentspecification are not limited in the number of first, second or thirdelectrodes 7, 8 27 which may be connected to the hereinbefore describedtouch controllers.

With few exceptions, the first, second, third and fourth touchcontrollers 44, 57, 97, 104 may also be used with any of the displaystack-ups or embedded stack ups described in connection with FIGS. 30Athrough to FIG. 45 of WO 2016/102975 A2.

Although the touch panels 43, 59, 64, 72 have been described havingelectrodes 7 generally arranged in rows or columns, however, eachelectrode 7, 8, 27 may instead take the form of a conductive padconnected to a touch controller by an individual conductive trace.

In the described first, second, third and fourth touch controllers 44,57, 97, 104, ADCs 50 a, 50 b, 89 are synchronised with one or morecapacitance signals which contain information relating to self- ormutual-capacitances of first and/or third electrodes 7, 27. For example,the ADCs 50 a, 50 b, 89 may be synchronised with an alternating signal17, V_(sig)(t), a capacitance measurement voltage signal V_(cap)(t), acapacitance drive signal 91, and/or a digitised amplified signal 54 a,54 b.

Referring, as an example, to the first or second touch controllers 44,57 in a case where mutual capacitance measurements are performed usingthe third electrodes 27 as transmitting, Tx, electrodes and the firstelectrodes 7 as receiving, Rx, electrodes. In such an example, thealternating signal 17, V_(sig)(t) is supplied to the first amplifiermodule 48 a, and the third electrodes 27 are driven with a capacitancemeasurement voltage signal V_(cap)(t) in the form of a drivingcapacitance measurement signal V_(drive)(t). It will be apparent that insome examples the alternating signal 17, V_(sig)(t) may be substantiallyidentical to the driving capacitance measurement signal V_(drive)(t).The first electrodes 7 pick-up a capacitance measurement voltage signalV_(cap)(t) in the form of a received capacitance measurement signalV_(receive)(t), which depends on the driving capacitance measurementsignal V_(drive)(t) and a mutual capacitance between first and thirdelectrodes 7, 27.

The primary ADCs 50 a, 50 b may be synchronised to one or more of thealternating signal 17, V_(sig)(t), the driving capacitance measurementsignal V_(drive)(t) or the received capacitance measurement signalV_(receive)(t). A synchronisation signal 53 may include an offset withrespect to the alternating signal 17, V_(sig)(t), the drivingcapacitance measurement signal V_(drive)(t) or the received capacitancemeasurement signal V_(receive)(t), with the offset determined accordingto the expected phase shifts φ corresponding to the range ofcapacitances expected/measured for the corresponding touch panel 43, 59,64, 72. It will be apparent that a synchronisation signal 53 determinedin this way has the effect of triggering sampling of the amplifiedsignals 14 a, 14 a at times when the amplitudes of the respectivedigitised amplified signals 54 a, 54 b are substantially equal to aground, common mode or minimum value.

In a further example, the synchronisation signal 53 may be determinedbased on the driving capacitance measurement signal V_(drive)(t), thereceived capacitance measurement signal V_(receive)(t), the amplifiedsignals 14 a, 14 b (which prior to sampling by the primary ADCs 50 a, 50b retain capacitance information) or the digitised amplified signals 54a, 54 b. For example, trigger circuitry (not shown) may determine acondition such as a falling edge or a peak value of a monitored signal,and the synchronisation signal 53 may be generated to trigger theprimary analog-to-digital converters 50 a, 50 b once a pre-set delay haselapsed since the condition of the trigger circuitry (not shown) wasmet. It will be apparent that a synchronisation signal 53 determined inthis way has the effect of triggering sampling of the amplified signals14 a, 14 a at times when the amplitudes of the respective digitisedamplified signals 54 a, 54 b are substantially equal to a ground, commonmode or minimum value, whether or not the trigger circuitry (not shown)monitors a digitised amplified signal 54 a, 54 b or another suitablecapacitance signal.

The primary analog-to-digital converters 50 a, 50 b have been describedas receiving the same synchronisation signal 53. However, this need notbe the case, and instead the first primary analog-to-digital converter50 a may receive a first synchronisation signal (not shown) whilst thesecond primary analog-to-digital converter 50 b receives a secondsynchronisation signal (not shown). The first and second synchronisationsignals (not shown) may be based on, and have different offsets withrespect to, a single capacitance signal, for example the alternatingsignal 17, V_(sig)(t), the driving capacitance measurement signalV_(drive)(t) or the received capacitance measurement signalV_(receive)(t). Alternatively, the first and second synchronisationsignals (not shown) may be based on different capacitance signals. Forexample, the first synchronisation signal (not shown) may be based onthe driving capacitance measurement signal V_(drive)(t), whilst thesecond synchronisation signal (not shown) may be based on the receivedcapacitance measurement signal V_(receive)(t). It will be apparent thatfirst and second synchronisation signals (not shown) determined in thisway have the effect of triggering sampling of the amplified signals 14a, 14 a at times when the amplitudes of the respective digitisedamplified signals 54 a, 54 b are substantially equal to a ground, commonmode or minimum value.

In still further examples, the first and second synchronisation signals(not shown) may be determined based on the driving capacitancemeasurement signal V_(drive)(t), the received capacitance measurementsignal V_(receive)(t), the amplified signals 14 a, 14 b, or thedigitised amplified signals 54 a, 54 b. For example, using triggercircuitry (not shown) as explained hereinbefore. In one example, thefirst synchronisation signal (not shown) may be generated in response toa falling edge or a peak value of the driving capacitance measurementsignal V_(drive)(t) or the corresponding first amplified signal 14 a,whilst the second synchronisation signal (not shown) is generated inresponse to a falling edge of peak value of the received capacitancemeasurement signal V_(receive)(t) or the corresponding second amplifiedsignal 14 b. It will be apparent that first and second synchronisationsignals (not shown) determined in this way have the effect of triggeringsampling of the amplified signals 14 a, 14 a at times when theamplitudes of the respective digitised amplified signals 54 a, 54 b aresubstantially equal to a ground, common mode or minimum value, whetheror not the trigger circuitry (not shown) monitors a digitised amplifiedsignal 54 a, 54 b or another suitable capacitance signal.

The hereinbefore described examples are equally applicable to the firstor second touch controllers 44, 57 in a case where mutual capacitancemeasurements are performed using the first electrodes 7 as driving, ortransmitting, Tx, electrodes and the third electrodes 27 as receiving,Rx, electrodes. The hereinbefore described examples are applicable byanalogy to the third and fourth touch controllers 97, 104. Inparticular, the synchronisation signal 90 which triggers theanalog-to-digital converter 89 may be based on any suitable capacitancesignal, including the alternating signal 17, V_(sig)(t), a capacitancemeasurement voltage signal V_(cap)(t) such as a driving capacitancemeasurement signal 91, V_(drive)(t) or a received capacitancemeasurement signal V_(receive)(t).

Alternative Capacitance Measurement Synchronisation Methods:

Examples have been described in which synchronisation of ADCs 50 withcapacitance signals 91, 92 is used for combined force and capacitancesensing. However, other forms of synchronisation with capacitancesignals 91, 92 are possible.

Seventh Touch-Panel System:

Referring also to FIG. 25, a seventh touch panel system 115 is shown.

The seventh touch panel system 115 includes the first touch panel 43 anda fifth touch controller 116 for combined pressure and capacitancesensing.

The first touch panel 43 may be bonded overlying the display 38 of anelectronic device 29. In this case, the materials of the first touchpanel 43 should be substantially transparent as described hereinbefore.A cover lens 46 may be bonded overlying the first touch panel 43. Thecover lens 46 is preferably glass but may be any transparent material.The cover lens 46 may be bonded to the first touch panel 43 using alayer of pressure sensitive adhesive (PSA) material 109. The layer ofPSA material 109 may be substantially transparent. The first and thirdelectrodes 7, 27 may be fabricated using index matching techniques tominimise visibility to a user.

The fifth touch controller 116 includes a capacitive touch controller84. The fifth touch controller 116 includes two signal processingchannels, each including a switch stage 117 a, 117 b, an amplificationstage 118 a, 118 b, a multiplexer 119 a, 119 b, and an ADC 120 a, 120 b.The fifth touch controller 116 also includes a controller 121. Thecontroller 121 may communicate with the processor 33 of the electronicdevice 29 using a link 32. The capacitive touch controller 84 has anumber of measurement ports 122 for output of a capacitance measurementsignal 91 and/or reception of a received signal 92. The switch stages 1u 7 a, 117 b each includes a number of switches SW, for exampletransistors, relays and so forth. The amplification stages 118 a, 118 beach include a number of charge amplifiers 123.

A number of terminals C1, . . . , C5 are connectable, and in use areconnected, to sensing electrodes in the form of the third electrodes 27of the first touch panel 43. Similarly, a number of terminals D1, . . ., D5 are connectable, and in use are connected, to sensing electrodes inthe form of the first electrodes 7 of the first touch panel 43.Alternatively, the terminals C1, . . . , C5 may be connectable/connectedto the first electrodes 7 and the terminals D1, . . . , D5 may beconnectable/connected to the third electrodes 27. Although fiveterminals C1, . . . , C5 and five terminals D1, . . . , D5 have beenillustrated, the number of terminals is not limited to five, and more orfewer terminals may be provided for connection to the sensing electrodes7, 27. A counter electrode in the form of the second electrode 8 isconnected to a fixed, common mode voltage V_(CM) (or system ground).

Each of the terminals C1, . . . , C5, D1, . . . , D5 is connected to oneof the measurement ports 122 of the capacitive touch controller 84.Optionally, the coupling of measurement ports 122 to the terminals C1, .. . , C5, D1, . . . , D5 may be via respective capacitances. Capacitivecoupling may be necessary when the impedance between pairs ofmeasurement ports 122 is low, which may lead to shorting of signalsgenerated by straining of the piezoelectric layer 9. However, when theinactive impedance between pairs of measurement ports 122 issufficiently large to prevent shorting of piezoelectric signals, thecapacitance may not be necessary and the coupling of measurement ports122 to respective terminals C1, . . . , C5, D1, . . . , D5 may bedirect.

Each of the terminals C1, . . . , C5, D1, . . . , D5 is also connectedto an input of one of the charge amplifiers 123 via a correspondingswitch SW of the switch stages 117 a, 117 b. The charge amplifiers 123output amplified signals 124 to the multiplexers 119 a, 119 b. Eachmultiplexer 119 a, 119 b selects one of the amplified signals 124 forinput to the corresponding ADC 120 a, 120 b. The ADCs 120 a, 120 bdigitise the amplified signals 124 and provide digitised signals 125 tothe controller 121. The controller 121 may process the digitised signals125 to convert them into force values. Alternatively, the controller 121may transfer the digitised signals 125 to the processor 33 via the link32 and the processor may convert digitised signals 125 into forcevalues.

Referring also to FIG. 26, the synchronisation performed by thecontroller 121 shall be explained.

The controller 121 outputs switch synchronisation signals 126, resetsynchronisation signals 127, and addressing signals 128. The controller121 may output an independent switch synchronisation signal 126 for eachSW of each switch stage 117 a, 117 b. Similarly, the controller 121 mayoutput an independent reset synchronisation signal 126 for each chargeamplifier 123 of each amplification stage 118 a, 118 b. The controller121 synchronises to an internal clocking signal 129. For example, theinternal clocking signal 129 may be a pulsed square wave as shown inFIG. 26, having period t₇−t₁ and duty cycle (t₅−t₁)/(t₇−t₁). Thesynchronisation may be triggered off the rising or falling edges of theinternal clocking signal 129. Consequently, the precise length t₅−t₁ ofpulses forming the internal clocking signal 129 is not important. Thecontroller 121 also outputs control signals 130 to the capacitive touchcontroller 84 to control the timing and sequencing for makingcapacitance measurements.

A single measurement cycle includes a first portion [t₁, t₂], and asecond portion [t₂, t₇]. In some examples, third or further portions maybe included in a measurement cycle, for example, a third portion maycorrespond to a display blanking interval. During the first portion [t₁,t₂] of the measurement cycle, the controller 121 uses the controlsignals 130 to cause the capacitive touch controller 84 to output acapacitance measurement signal 91 to one or more of the third electrodes27 via the respective terminals C1, . . . , C5. During the first portion[t₁, t₂] the capacitive touch controller 84 also monitors, via terminalsD1, . . . , D5, received signals 92 from one or more of the firstelectrodes 7. The first portion [t₁, t₂] is preferably long enough toencompass two or more periods of the capacitance measurement signal 91.During the first portion [t₁, t₂], the charge amplifiers 123 of theamplification stages 118 a, 118 b are disconnected from the terminalsC1, . . . , C5, D1, . . . , D5 by the respective switches SW of theswitch stages 117 a, 117 b. This is illustrated in FIG. 26 by the lowlevel of the switch synchronisation signal 126, indicating an open(non-conductive) state of a switch SW.

During the second portion [t₂, t₇] of the measurement cycle, thecontroller 121 uses the control signals 130 to cause the capacitivetouch controller 84 to stop outputting the capacitance measurementsignal 91 via any of the measurement ports 122. During the secondportion [t₂, t₇], one or more of the charge amplifiers 123 are connectedto the corresponding terminals C1, . . . , C5, D1, . . . , D5 by therespective switches SW. This is illustrated in FIG. 26 by the high levelof the switch synchronisation signal 126, indicating a closed(conductive) state of a switch SW. During the second portion [t₂, t₇,],the controller 121 uses the addressing signals 228 to cause themultiplexers 119 a, 119 b to scan through the outputs of each chargeamplifier 123 of the amplification stages 118 a, 118 b.

In this way, the capacitive touch controller 84 may perform mutualcapacitance measurements during the first portion [t₁, t₂], whilstforces may be sensed based on charges accumulated by the chargeamplifiers 123 during the second portion [t₂, t₇]. Alternatively, thecapacitive touch controller 84 may perform self-capacitance measurementsfor each of the sensing electrodes in the form of first and thirdelectrodes 7, 27.

Example of Charge Amplifiers:

Referring also to FIG. 27, an example of one configuration of the chargeamplifiers 123 and switch stages 117 a, 117 b for the fifth touchcontroller 116 is shown.

In this example configuration, each charge amplifier 123 forming part ofthe amplification stages 118 a, 118 b includes an operational amplifierOP having an inverting input, a non-inverting input and an output. Theinverting input of each operational amplifier OP is coupled to acorresponding sensing electrode 7, 27 via a respective terminal C1, . .. , C5, D1, . . . , D5 (not illustrated in FIG. 27 for simplicity) and aswitch SW, labelled SW1 for reference in FIG. 27. Each sensing electrode7, 27 is also connected to a measurement port 122 of the capacitivetouch controller 84. The paths to charge amplifiers 123 and measurementports 122 divide at a node 131. Optionally, an input resistance Rb, maybe connected in series between the node 131 and the switch SW1. When theimpedance between pairs of measurement ports 122 is high, directconnection to the node 131 may be possible. However, when the impedancebetween pairs of measurement ports 122 is insufficient to preventshorting of charges induced by the layer of piezoelectric material 9,the measurement ports 122 may be AC coupled to the corresponding nodes131 via capacitances C₁.

The non-inverting input of the operational amplifier OP is connected toa common mode voltage V_(CM). A feedback network of the charge amplifier100 includes a feedback capacitance C_(f) and a second switch SW2connected in parallel between the inverting input and the output of theoperational amplifier OP. Optionally, the feedback network may alsoinclude a feedback resistance R_(f). The output of the operationalamplifier provides the amplified signal 124.

Other terminals of the operational amplifier OP, such as power supplyterminals, may be present, but are not shown in this or other schematiccircuit diagrams described herein.

During the first portion [t₁, t₂] of the measurement cycle, the switchsynchronisation signal 126 controls the switch SW1 to be open(non-conductive state), and the control signals 130 cause the capacitivetouch controller 84 to output a capacitance measurement signal 91 ormonitor a received signal 92 as appropriate. The disconnection of theswitch SW1 prevents the capacitance measurement signal 91 or receivedsignal 92 from coupling to the charge amplifier 123 in order to maintainthe charge amplifier 123 at zero offset in preparation for the secondportion [t₂, t₇]. Additionally, the disconnection of the switch SW1during the first portion [t₁, t₂] may prevent the charge amplifier(s)123 from loading the capacitive touch controller 84 and influencing thecapacitance measurements. During the first portion [t₁, t₂], the resetsynchronisation signal 127 holds the second switch SW2 closed(conductive state) to short (discharge) the feedback capacitor C_(f) andprevent charge accumulation during the first portion [t₁, t₂]. Closureof the second switch SW2 during the first portion [t₁, t₂] may preventany leakage current across the switch SW1 from being accumulated on thefeedback capacitor C_(f). In this way, the charge amplifier 123 may beprevented from acquiring unwanted DC-offset during the first portion[t₁, t₂].

During the second portion [t₂, t₇], the control signals 130 cause thecapacitive touch controller 84 to cease outputting capacitancemeasurement signals 91 via any of the measurement ports 122, and theswitch synchronisation signal 126 causes the switch SW1 to become closed(conductive state). The second switch SW2 is held closed for a shorttime after the start of the second portion [t₂, t₇], and the resetsynchronisation signal 127 controls the second switch to become open(non-conductive state) at a time t₃>t₂. The delay t₃−t₂ may berelatively short, and may prevent noise during the switchover betweenthe first portion [t₁, t₂] and second portion [t₂, t₇] from beingerroneously detected as signals from the piezoelectric layer 9.Additionally, the delay t₃−t₂ may allow time for any charges induced onthe sensing electrodes 7, 27 during the first portion [t₁, t₂] todissapate. The length of the delay t₃−t₂ may depend on an RC constant ofthe sensing electrodes 7, 27.

By holding the charge amplifiers 123 to zero during the first portion[t₁, t₂] and the switchover to the second portion [t₂, t₇], noise in theamplified signal 124 output may be avoided. Additionally, because thecharge amplifiers 123 do not need to accommodate residual, attenuatedcapacitance signals 91, 92, the gain of the charge amplifiers 123 may beset relatively higher without comprising integrity of the force sensing.

Optionally, drift of the operational amplifier OP output during thesecond portion [t₂, t₇] may be suppressed by briefly discharging thefeedback capacitor C using the second switch SW2 at one or more pointsduring the second portion [t₂, t₇]. For example, the resetsynchronisation signal 127 may cause the second switch SW2 to becomeclosed (conductive) at times t₄, t₅, and t₆ between t₂ and t₇.

Example Measurement Sequence:

A full readout of capacitance values and/or force signals for the wholefirst touch panel 43 may be spread across multiple measurement cycles.

For example, referring in particular to FIG. 25, one example sequenceshall be described.

In a first measurement cycle, the capacitive touch controller 84 maydrive the third electrode 27 coupled to terminal C1 with the capacitancemeasurement signal 91, whilst monitoring received signals 92 on each ofthe first electrodes 7 via terminals D1, . . . , D5. In this way, mutualcapacitance measurements corresponding to an entire row or column ofintersections between first and third electrodes 7, 27 may be obtainedduring the first portion [t₁, t₂] of the first measurement cycle. As oneexample of possible timings, the first portion [t₁, t₂] may have aduration of t₂−t₁=100 μs.

Subsequently, during the second portion [t₂, t₇] of the firstmeasurement cycle, the multiplexers 119 a, 119 b may be used to scanthrough the amplified signals 124 from the amplification stages 118 a,118 b. The outputs of charge amplifiers 123 will store the accumulatedcharges until addressed by a multiplexer 119 a, 119 b. The amplifiedsignals 124 may be scanned several times during the second portion [t₂,t₇], or alternatively, each amplified signal 124 may be read out onceduring the second portion [t₂, t₇] (for example towards the end of thesecond portion [t₂, t₇]). In this way, force signals corresponding toeach sensing electrode 7, 27 may be read during every measurement cycle.This may help to avoid missing the transient signals generated by thepiezoelectric layer 9, which correspond to changes in applied force. Inother examples, readout of force signals may be spread across two ormore measurement cycles. As one example of possible timings, the secondportion [t₂, t₇] may have a duration of t₇−t₂=500 μs.

During the first portion [t₁, t₂] of a second measurement cycle, thecapacitive touch controller 84 drives the third electrode 27 connectedto the terminal C2 with the capacitance measurement signal 91, whilstmonitoring received signals 92 on each of the first electrodes 7 viaterminals D1, . . . , D5. In this way, mutual capacitance measurementscorresponding to the next row or column of intersections between firstand third electrodes 7, 27 may be obtained. During the second portion[t₂, t₇], force signals corresponding to each sensing electrode 7, 27are again obtained.

This process continues for terminals C3, C4 and C5 before repeating. Thesequence may be readily scaled to touch panels having any number offirst and third electrodes 7, 27.

The described sequence is not essential, and any suitable predeterminedor dynamically determined sequence may be employed in order to obtainmutual capacitance measurements from the entire first touch panel 43.

For example, in some implementations a single measurement cycle mayinclude obtaining measurements of all capacitance values and all forcesignals. The first portion [t₁, t₂] may be long enough, for example 3ms, to permit scanning every intersection of first and third electrodes7, 27. In other words, the capacitive touch controller 84 may drive eachof the terminals C1, . . . , C5 in turn, whilst monitoring terminals D1,. . . , D5. The second portion [t₂, t₇] may also be lengthened, forexample to 15 ms, to allow a longer period of charge accumulation.

In other examples, the capacitive touch controller 84 may performself-capacitance measurements of the first and third electrodes 7, 27individually. In such examples, sensing electrodes 7, 27 may be drivenwith capacitance measurement signals 91 either individually, or ingroups.

The capacitive touch controller 84 does not need to be a separate modulewithin the fifth touch controller 116, and alternatively may beintegrated with the controller 121. In other examples, the capacitivetouch controller 84 may be provided separately from the fifth touchcontroller 116, which may facilitate augmenting an existing projectedcapacitance touch system with pressure sensing on one or both of x- andy-electrodes.

The fifth touch controller 116 may alternatively be used with the thirdor fourth touch panels 64, 72 instead of the first touch panel 43.

Although illustrated with separate signal processing channels for thefirst and third electrodes 7, 27, this is not essential. In someexamples, a single switch stage 117, and a single amplification stage118 may be used. The amplified signals 124 may be multiplexed to asingle ADC 120, or alternatively two or more multiplexers 119 andcorresponding ADCs 120 may be used to reduce delays between samplingeach amplified signal 124.

Eighth Touch-Panel System:

Referring also to FIG. 28, an eighth touch panel system 132 is shown.

The eighth touch panel system 132 includes the first touch panel 43 anda sixth touch controller 133 for combined pressure and capacitancesensing.

The sixth touch controller 133 is the same as the fifth touch controller116, except that the sixth touch controller 133 does not include themultiplexers 119 a, 119 b or ADCs 120 a, 120 b, and replaces thecontroller 121 with a controller 134 which includes analog input ports135. Each analog input port 135 of the controller 134 is associated withan ADC integrated within the controller 134. In this way, the amplifiedsignals 124 from each charge amplifier 123 may be monitoredconcurrently.

The capacitive touch controller 84 of the sixth touch controller 133 mayperform mutual capacitance measurements and/or self-capacitancemeasurements.

The capacitive touch controller 84 does not need to be a separate modulewithin the sixth touch controller 133, and alternatively may beintegrated with the controller 134. In other examples, the capacitivetouch controller 84 may be provided separately from the sixth touchcontroller 133, which may facilitate augmenting an existing projectedcapacitance touch system with pressure sensing on one or both of x- andy-electrodes.

The sixth touch controller 116 may alternatively be used with the thirdor fourth touch panels 64, 72 instead of the first touch panel 43.

Although illustrated with separate signal processing channels for thefirst and third electrodes 7, 27, this is not essential. In someexamples, a single switch stage 117, and a single amplification stage 18may be used.

Although five terminals C1, . . . , C5 and five terminals D1, . . . , D5have been illustrated, the number of terminals is not limited to five,and more or fewer terminals may be provided for connection to thesensing electrodes 7, 27.

Ninth Touch Panel System:

Referring also to FIG. 29, a ninth touch panel system 136 is shown.

The ninth touch panel system 132 includes a fifth touch panel 137 and aseventh touch controller 138 for combined pressure and capacitancesensing.

The seventh touch controller 138 is the same as the sixth touchcontroller 133, except that a single switch stage 117 and a singleamplification stage 118 are used. Each charge amplifier 123 is coupledto a corresponding terminal A1, . . . , A9. Each terminal A1, . . . , A9is also connected to the capacitive touch controller 84. Althoughillustrated as including capacitors between the measurement ports 122and the terminals A1, . . . , A9, capacitors will not be required if theimpedance between pairs of measurement ports 122 is sufficiently largeto avoid shorting between sensing electrodes 7 when the capacitive touchcontroller 84 is not active during the second portion [t₂, t₇].

The fifth touch panel 137 does not include third electrodes 27 or thesecond layer structure 24. Instead, a co-extensive second electrode 8 isprovided below the second face 6 of the first layer structure 4, and anumber of first electrodes 7 are disposed on or over the first face 5 ofthe first layer structure 4. The first electrodes 7 are in the form ofdiscrete pads, and the first electrodes 7 are arranged to form an arrayor grid over the first face 5. Each sensing electrode in the form of afirst electrode 7 is connected to a corresponding terminal A₁, . . . ,A₉ of the seventh touch controller 138. The counter (or common)electrode in the form of the second electrode 8 is connected to a fixed,common mode (or system ground) voltage V_(CM).

Unlike the seventh or eighth touch panel systems 115, 132, which usedthe first touch panel 43, the fifth touch panel 137 is only suitable forself-capacitance measurements. Otherwise, the functions are identical,with capacitance measurement signals 91 supplied to one or more firstelectrodes 7 during the first portion [t₁, t₂] of each measurementcycle.

The capacitive touch controller 84 does not need to be a separate modulewithin the seventh touch controller 138, and alternatively may beintegrated with the controller 134. In other examples, the capacitivetouch controller 84 may be provided separately from the seventh touchcontroller 138, which may facilitate augmenting an existing projectedcapacitance touch system with pressure sensing on one or both of x- andy-electrodes.

Although nine terminals A1, . . . , A9 have been illustrated, the numberof terminals is not limited to nine, and more or fewer terminals may beprovided for connection to the sensing electrodes 7.

The fifth touch panel 137 may be bonded overlying the display 38 of anelectronic device 29. In this case, the materials of the fifth touchpanel 137 should be substantially transparent as described hereinbefore.A cover lens 46 may be bonded overlying the fifth touch panel 137. Thecover lens 46 is preferably glass but may be any transparent material.The cover lens 46 may be bonded to the fifth touch panel 137 using alayer of pressure sensitive adhesive (PSA) material 109. The layer ofPSA material 109 may be substantially transparent. The first electrodes7 may be fabricated using index matching techniques to minimisevisibility to a user.

Tenth Touch Panel System:

Referring also to FIG. 30, a tenth touch panel system 139 is shown.

The tenth touch panel system 139 includes the first touch panel 43 andan eighth touch controller 140 for combined pressure and capacitancesensing.

The eighth touch controller 140 is the same as the fifth touchcontroller 116, except that the order of multiplexing and amplificationis reversed. In the eighth touch controller 140, each terminal C1, . . ., C5 is connected to an input of multiplexer 119 a and each terminal D1,. . . , D5 is connected to an input of multiplexer 119 b. Eachmultiplexer 119 a, 119 b output is connected to a corresponding chargeamplifier 123. The multiplexers 119 a, 119 b are controlled by theswitch synchronisation signal 126 to disconnect all of the terminals C1,. . . , C5, D1, . . . , D5 from the charge amplifiers 123 during thefirst portion [t₁, t₂] of each measurement cycle. Consequently, there isno need for separate switch stages 117 a, 117 b. During the secondportion [t₂, t₇] of the measurement cycle, the switch synchronisationsignals 126 control the order of addressing the third electrodes 27 andthe order of addressing the first electrodes 7.

In other examples, the multiplexers 119 a, 119 b need not be n-to-1multiplexers (with n an integer). Instead, n-to-m multiplexers may beused (with m an integer) in combination with m charge amplifiers 123 inorder to reduce the time needed to scan all of the sensing electrodes 7,27.

Referring also to FIG. 31, an example of one configuration of the chargeamplifiers 123 and multiplexers 119 a, 119 b is shown for the eighthtouch controller 140.

The charge amplifier 123 is configured the same as for each of thecharge amplifiers 123 of the fifth touch controller 116 (FIG. 27),except that the inverting input of the operational amplifier OP isconnected to a sensing electrode 7, 27 via a multiplexer 119 a, 119 b.

The capacitive touch controller 84 of the eighth touch controller 140may perform mutual capacitance measurements and/or self-capacitancemeasurements.

The capacitive touch controller 84 does not need to be a separate modulewithin the eighth touch controller 1400, and alternatively may beintegrated with the controller 121. In other examples, the capacitivetouch controller 84 may be provided separately from the eighth touchcontroller 140, which may facilitate augmenting an existing projectedcapacitance touch system with pressure sensing on one or both of x- andy-electrodes.

The eighth touch controller 140 may alternatively be used with the thirdor fourth touch panels 64, 72 instead of the first touch panel 43.

Although illustrated with separate signal processing channels for thefirst and third electrodes 7, 27, this is not essential. In someexamples, a single multiplexer 119 may be used.

Although five terminals C1, . . . , C5 and five terminals D1, . . . , D5have been illustrated, the number of terminals is not limited to five,and more or fewer terminals may be provided for connection to thesensing electrodes 7, 27.

In some examples, the ADCs 120 a, 120 b may be omitted and thecontroller 121 may be replaced with the controller 134 having analoginput ports 135.

Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel features orany novel combination of features disclosed herein either explicitly orimplicitly or any generalization thereof, whether or not it relates tothe same invention as presently claimed in any claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention. The applicant hereby gives notice that new claims maybe formulated to such features and/or combinations of such featuresduring the prosecution of the present application or of any furtherapplication derived therefrom.

What is claimed is:
 1. A device for processing signals from a projectedcapacitance touch panel, the touch panel comprising a layer ofpiezoelectric material disposed between a plurality of sensingelectrodes and at least one counter electrode, the device comprising: acapacitive touch controller having a plurality of measurement ports; aplurality of charge amplifiers; a plurality of terminals for connectionto the sensing electrodes of the projected capacitance touch panel,wherein each terminal is connected to one of the measurement ports andeach terminal is also connected to an input of one of the chargeamplifiers via a corresponding switch of a plurality of switches; acontroller configured to synchronise the capacitive touch controller andthe plurality of switches so that: during a first portion of a cycle thecapacitive touch controller outputs a capacitance measurement signal toone or more of the terminals, and the plurality of charge amplifiers aredisconnected from the terminals by the respective switches; and during asecond portion of the cycle the capacitive touch controller does notoutput the capacitance measurement signal, and one or more of the chargeamplifiers are connected to the corresponding terminals by therespective switches; wherein each charge amplifier is an integratingamplifier, and wherein each integrating amplifier which is connected bythe respective switch to the corresponding terminal is reset one or moretimes during the second portion of the cycle.
 2. A device according toclaim 1, wherein during the second portion of the cycle, each of thecharge amplifiers is connected to the corresponding terminal by therespective switch.
 3. A device according to claim 1, wherein thecapacitive touch controller is configured to measure capacitance valueswhen the device is connected to the projected capacitance touch panel.4. A device according to claim 1, wherein the controller is configuredto measure force signals based on outputs from the charge amplifierswhen the device is connected to the projected capacitance touch panel.5. A system comprising: a projected capacitance touch panel comprising alayer of piezoelectric material disposed between a plurality of sensingelectrodes and at least one second electrode; and a device according toclaim 1; wherein each sensing electrode of the touch panel is connectedto a corresponding terminal of the device.
 6. A system according toclaim 5, wherein the plurality of sensing electrodes comprises: aplurality of first sensing electrodes, each first sensing electrodeextending in a first direction and the plurality of first sensingelectrodes spaced apart in a second direction, wherein the seconddirection is different to the first direction; a plurality of secondsensing electrodes, each second sensing electrode extending in thesecond direction and the plurality of second sensing electrodes spacedapart in the first direction; wherein the first and second sensingelectrodes are electrically insulated from one another.
 7. A systemaccording to claim 5, wherein the plurality of sensing electrodescomprise a plurality of sensing pads disposed to form an array.
 8. Adevice for processing signals from a projected capacitance touch panel,the touch panel comprising a layer of piezoelectric material disposedbetween a plurality of sensing electrodes and at least one counterelectrode, the device comprising: a controller having a plurality ofmeasurement ports, wherein the controller is configured to output acapacitance measurement signal via one or more of the measurement ports;a plurality of charge amplifiers; a plurality of terminals forconnection to the sensing electrodes of the projected capacitance touchpanel, wherein each terminal is connected to one of the measurementports and each terminal is also connected to one of the chargeamplifiers via a corresponding switch of a plurality of switches;wherein the controller is further configured to synchronise theplurality of switches with the output of the capacitance measurementsignal so that: during a first portion of a cycle the controller outputsa capacitance measurement signal to one or more terminals, and theplurality of charge amplifiers are disconnected from the correspondingterminals by the respective switches; and during a second portion of thecycle the controller does not output the capacitance measurement signal,and one or more of the charge amplifiers are connected to thecorresponding terminals by the respective switches; wherein each chargeamplifier is an integrating amplifier, and wherein each integratingamplifier which is connected by the respective switch to thecorresponding terminal is reset one or more times during the secondportion of the cycle.
 9. A device according to claim 8, wherein duringthe second portion of the cycle, each of the charge amplifiers isconnected to the corresponding terminal by the respective switch.
 10. Adevice according to claim 8, wherein the controller is configured tomeasure capacitance values using the capacitance measurement signal whenthe device is connected to the projected capacitance touch panel.
 11. Adevice according to claim 8, wherein the controller is configured tomeasure force signals based on outputs from the charge amplifiers whenthe device is connected to the projected capacitance touch panel.
 12. Asystem comprising: a projected capacitance touch panel comprising alayer of piezoelectric material disposed between a plurality of sensingelectrodes and at least one second electrode; and a device according toclaim 8; wherein each sensing electrode of the touch panel is connectedto a corresponding terminal of the device.
 13. A system according toclaim 12, wherein the plurality of sensing electrodes comprises: aplurality of first sensing electrodes, each first sensing electrodeextending in a first direction and the plurality of first sensingelectrodes spaced apart in a second direction, wherein the seconddirection is different to the first direction; a plurality of secondsensing electrodes, each second sensing electrode extending in thesecond direction and the plurality of second sensing electrodes spacedapart in the first direction; wherein the first and second sensingelectrodes are electrically insulated from one another.
 14. A systemaccording to claim 12, wherein the plurality of sensing electrodescomprise a plurality of sensing pads disposed to form an array.
 15. Amethod employing a projected capacitance touch panel, the touch panelcomprising a layer of piezoelectric material disposed between aplurality of sensing electrodes and at least one counter electrode, themethod comprising: applying a capacitance measurement signal to one ormore of the sensing electrodes during a first portion of a cycle;causing a plurality of switches to be open during the first portion ofthe cycle, wherein each of the switches connects one of the sensingelectrodes to a corresponding charge amplifier, wherein each chargeamplifier is an integrating amplifier; stopping application of thecapacitance measurement signal during a second portion of the cycle; andconnecting one or more of the sensing electrodes to the correspondingcharge amplifiers during the second portion of the cycle, using therespective switches; wherein the method further includes resetting eachintegrating amplifier one or more times during the second portion of thecycle.
 16. A method according to claim 15, further comprising measuringone or more capacitance values based on the capacitance measurementsignal during the first portion of the cycle.
 17. A method according toclaim 15, further comprising measuring force signals based on outputsfrom the charge amplifiers during the second portion of the cycle.